Running:

NetBSD pimin 3.0.1 NetBSD 3.0.1 (PIMIN.MP) #0: Sun Sep 10 20:06:49 PDT 2006  
      root@bigbox.rockhead.com:/usr/src/sys/arch/i386/compile/PIMIN.MP i386

Why does traceroute pick tlp0 as the interface to try?
The default route seems more reasonable to me??

Routing tables

Internet:
Destination        Gateway            Flags     Refs     Use    Mtu  Interface
default            10.58.54.15        UGS         1       23      -  tun0
10.57.158.105      10.58.54.79        UGHS        0        0      -  tun0
10.57.158.136      10.58.54.79        UGHS        0      108      -  tun0
10.58.54.15        10.58.54.15        UH          1        0      -  tun0
127/8              127.0.0.1          UGRS        0        0  33192  lo0
127.0.0.1          127.0.0.1          UH          1     1402  33192  lo0
172.16.80/20       link#1             UC          3        0      -  tlp0
172.16.89.42       00:40:05:36:73:53  UHLc        2    33401      -  lo0
172.16.89.45       00:0f:b5:f9:0d:9c  UHLc        8    86501      -  tlp0
172.16.89.48       00:18:4d:72:15:60  UHLc       18   617334      -  tlp0
192.168/16         link#1             UC          0        0      -  tlp0

pimin[root]: route get 10.57.158.136
   route to: 10.57.158.136
destination: 10.57.158.136
    gateway: 10.58.54.79
 local addr: 10.58.54.79
  interface: tun0
      flags: <UP,GATEWAY,HOST,DONE,STATIC>
 recvpipe  sendpipe  ssthresh  rtt,msec    rttvar  hopcount      mtu     expire
       0         0         0         0         0         0         0         0 

pimin[root]: traceroute 10.57.158.136
traceroute: Warning: Multiple interfaces found; using 172.16.89.42 @ tlp0
traceroute to 10.57.158.136 (10.57.158.136), 64 hops max, 40 byte packets

TIA,
Paul N.