I think I am starting to get a handle on the TCP/IP stalling problem.
I have now observed the problem not just with telnet but also in mail
transfers. After observing it with tcpdump, I have found what appears to be
the common factor:

   Connections which work do not have a timestamp option in each packet.
Connections which do not work have a timestamp option in each packet.
Here's some logs:

This is a failing connection:

09:41:10.590001 carfallin.picarefy.com.51592 > ringtail.fur.com.2069: S [tcp sum ok] 435129345:435129345(0) win 16384 <mss 1460,nop,wscale 0,nop,nop,timestamp 2213213 0> [tos 0x10] (ttl 64, id 55025)
09:41:10.720001 ringtail.fur.com.2069 > carfallin.picarefy.com.51592: S [tcp sum ok] 2706067873:2706067873(0) ack 435129346 win 16060 <mss 1460,nop,nop,timestamp 1350717946 2213213,nop,wscale 0> (DF) (ttl 48, id 42326)
09:41:10.720002 carfallin.picarefy.com.51592 > ringtail.fur.com.2069: . [tcp sum ok] ack 1 win 17520 <nop,nop,timestamp 2213213 1350717946> [tos 0x10] (ttl 64, id 55026)
09:41:10.890001 ringtail.fur.com.2069 > carfallin.picarefy.com.51592: P [tcp sum ok] 1:12(11) ack 1 win 16060 <nop,nop,timestamp 1350717960 2213213> (DF) (ttl 48, id 42331)
09:41:11.040001 ringtail.fur.com.2069 > carfallin.picarefy.com.51592: P 12:760(748) ack 1 win 16060 <nop,nop,timestamp 1350717960 2213213> (DF) (ttl 48, id 42332)
09:41:11.040002 carfallin.picarefy.com.51592 > ringtail.fur.com.2069: . [tcp sum ok] ack 760 win 16772 <nop,nop,timestamp 2213214 1350717960> [tos 0x10] (ttl 64, id 55027)
09:41:14.010001 ringtail.fur.com.2069 > carfallin.picarefy.com.51592: P 1:760(759) ack 1 win 16060 <nop,nop,timestamp 1350718260 2213213> (DF) (ttl 48, id 42372)
09:41:14.010002 carfallin.picarefy.com.51592 > ringtail.fur.com.2069: . [tcp sum ok] ack 760 win 17520 <nop,nop,timestamp 2213220 1350717960> [tos 0x10] (ttl 64, id 55028)
09:41:16.080001 carfallin.picarefy.com.51592 > ringtail.fur.com.2069: P [tcp sum ok] 1:6(5) ack 760 win 17520 <nop,nop,timestamp 2213224 1350717960> [tos 0x10] (ttl 64, id 55029)
09:41:16.980001 carfallin.picarefy.com.51592 > ringtail.fur.com.2069: P [tcp sum ok] 1:6(5) ack 760 win 17520 <nop,nop,timestamp 2213225 1350717960> [tos 0x10] (ttl 64, id 55030)
09:41:17.190001 ringtail.fur.com.2069 > carfallin.picarefy.com.51592: P 760:1262(502) ack 6 win 16060 <nop,nop,timestamp 1350718583 2213225> (DF) (ttl 48, id 42404)
09:41:17.300001 carfallin.picarefy.com.51592 > ringtail.fur.com.2069: . [tcp sum ok] ack 1262 win 17520 <nop,nop,timestamp 2213226 1350718583> [tos 0x10] (ttl 64, id 55031)
09:41:17.330001 ringtail.fur.com.2069 > carfallin.picarefy.com.51592: P 1262:2010(748) ack 6 win 16060 <nop,nop,timestamp 1350718584 2213225> (DF) (ttl 48, id 42405)
09:41:17.500001 carfallin.picarefy.com.51592 > ringtail.fur.com.2069: . [tcp sum ok] ack 2010 win 17520 <nop,nop,timestamp 2213227 1350718584> [tos 0x10] (ttl 64, id 55032)

   At this point it just hangs, forever, even though there is more data to
send.

This connection, on the other hand, works fine:

09:49:11.670001 carfallin.picarefy.com.51577 > newsys.furry.org.8888: S [tcp sum ok] 1782755745:1782755745(0) win 16384 <mss 1460,nop,wscale 0,nop,nop,timestamp 2214175 0> [tos 0x10] (ttl 64, id 55348)
09:49:11.910001 newsys.furry.org.8888 > carfallin.picarefy.com.51577: S [tcp sum ok] 1395111365:1395111365(0) ack 1782755746 win 32736 <mss 1460> (ttl 50, id 62839)
09:49:11.910002 carfallin.picarefy.com.51577 > newsys.furry.org.8888: . [tcp sum ok] ack 1 win 17520 [tos 0x10] (ttl 64, id 55349)
09:49:12.180001 newsys.furry.org.8888 > carfallin.picarefy.com.51577: P [tcp sum ok] 1:13(12) ack 1 win 32736 (DF) [tos 0x10] (ttl 50, id 62845)
09:49:12.330001 carfallin.picarefy.com.51577 > newsys.furry.org.8888: . [tcp sum ok] ack 13 win 17520 [tos 0x10] (ttl 64, id 55350)
09:49:12.700001 newsys.furry.org.8888 > carfallin.picarefy.com.51577: P 13:967(954) ack 1 win 32736 (DF) [tos 0x10] (ttl 50, id 62849)
09:49:12.730001 carfallin.picarefy.com.51577 > newsys.furry.org.8888: . [tcp sum ok] ack 967 win 17520 [tos 0x10] (ttl 64, id 55351)
09:49:16.820001 carfallin.picarefy.com.51577 > newsys.furry.org.8888: P [tcp sum ok] 1:6(5) ack 967 win 17520 [tos 0x10] (ttl 64, id 55352)
09:49:17.010001 newsys.furry.org.8888 > carfallin.picarefy.com.51577: . [tcp sum ok] ack 6 win 32736 (DF) [tos 0x10] (ttl 50, id 62949)
09:49:17.080001 newsys.furry.org.8888 > carfallin.picarefy.com.51577: P [tcp sum ok] 967:1012(45) ack 6 win 32736 (DF) [tos 0x10] (ttl 50, id 62950)
09:49:17.130001 carfallin.picarefy.com.51577 > newsys.furry.org.8888: . [tcp sum ok] ack 1012 win 17520 [tos 0x10] (ttl 64, id 55353)
09:49:17.340001 newsys.furry.org.8888 > carfallin.picarefy.com.51577: P 1012:2472(1460) ack 6 win 32736 (DF) [tos 0x10] (ttl 50, id 62951)
09:49:17.340002 carfallin.picarefy.com.51577 > newsys.furry.org.8888: . [tcp sum ok] ack 2472 win 17084 [tos 0x10] (ttl 64, id 55354)
09:49:17.600001 newsys.furry.org.8888 > carfallin.picarefy.com.51577: P 2472:3932(1460) ack 6 win 32736 (DF) [tos 0x10] (ttl 50, id 62952)
09:49:17.600002 carfallin.picarefy.com.51577 > newsys.furry.org.8888: . [tcp sum ok] ack 3932 win 17084 [tos 0x10] (ttl 64, id 55355)
09:49:17.840001 newsys.furry.org.8888 > carfallin.picarefy.com.51577: P 3932:5392(1460) ack 6 win 32736 (DF) [tos 0x10] (ttl 50, id 62953)
09:49:17.840002 carfallin.picarefy.com.51577 > newsys.furry.org.8888: . [tcp sum ok] ack 5392 win 17084 [tos 0x10] (ttl 64, id 55356)
09:49:18.110001 newsys.furry.org.8888 > carfallin.picarefy.com.51577: P 5392:6852(1460) ack 6 win 32736 [tos 0x10] (ttl 50, id 62971)
09:49:18.130001 carfallin.picarefy.com.51577 > newsys.furry.org.8888: . [tcp sum ok] ack 6852 win 15831 [tos 0x10] (ttl 64, id 55357)
09:49:18.350001 newsys.furry.org.8888 > carfallin.picarefy.com.51577: P 6852:8312(1460) ack 6 win 32736 [tos 0x10] (ttl 50, id 62972)
09:49:18.530001 carfallin.picarefy.com.51577 > newsys.furry.org.8888: . [tcp sum ok] ack 8312 win 15393 [tos 0x10] (ttl 64, id 55358)
09:49:18.580001 newsys.furry.org.8888 > carfallin.picarefy.com.51577: P 8312:9772(1460) ack 6 win 32736 [tos 0x10] (ttl 50, id 62973)
09:49:18.730001 carfallin.picarefy.com.51577 > newsys.furry.org.8888: . [tcp sum ok] ack 9772 win 13933 [tos 0x10] (ttl 64, id 55359)
09:49:19.020001 newsys.furry.org.8888 > carfallin.picarefy.com.51577: P 9772:10347(575) ack 6 win 32736 (DF) [tos 0x10] (ttl 50, id 62996)
09:49:19.130001 carfallin.picarefy.com.51577 > newsys.furry.org.8888: . [tcp sum ok] ack 10347 win 13358 [tos 0x10] (ttl 64, id 55360)
09:49:19.530001 carfallin.picarefy.com.51577 > newsys.furry.org.8888: . [tcp sum ok] ack 10347 win 14382 [tos 0x10] (ttl 64, id 55361)
09:49:20.600001 carfallin.picarefy.com.51577 > newsys.furry.org.8888: . [tcp sum ok] ack 10347 win 15406 [tos 0x10] (ttl 64, id 55362)
09:49:21.660001 carfallin.picarefy.com.51577 > newsys.furry.org.8888: . [tcp sum ok] ack 10347 win 16431 [tos 0x10] (ttl 64, id 55363)
09:49:22.730001 carfallin.picarefy.com.51577 > newsys.furry.org.8888: . [tcp sum ok] ack 10347 win 17455 [tos 0x10] (ttl 64, id 55364)

   Unfortunately, with my limited knowledge of TCP/IP, I don't really know
what the timestamp option is, or what exactly the numbers mean, or why they
might cause the transmission to stall.

   Help?! I suppose if nothing else I could go into the kernel and figure
out how to disable timestamping on IP, but I'd rather know what's wrong.

   --James