This seems to me that the kernel is too big for your machine.
I had very much similar problem on StarMax 3000/240, 4000/160 etc.
Kernel is now loaded starting 1M Bytes boundary. Your new kernel
is beyond 3MB in size. And unfortunately, OF of some type of machines uses
starting at 4MB boundary.
(This is what I have heard and not saying with full (or any) understanding).

You may have two options to work arround this problem.
(1)
Get small kernel, less than 3M. There are so many USB drivers etc.
It seems to me easy to get such a kernel.

(2) 
Change the kernel loading base. In my case,

> setenv real-base F00000
> reset-all
works.
Good luck,

From: Jake Luck <netbsd@10k.org>
Subject: Re: mesh driver
Date: Sun, 13 Aug 2000 00:09:56 -0400 (EDT)
Message-ID: <Pine.SOL.4.21.0008130002440.3630-100000@matrix.10k.org>

n> i just rebuilt today (8/13)'s kernel. and the kernel crashes on boot
 
n> >> NetBSD/macppc OpenFirmware Boot, Revision 1.2
n> >> (root@death, Thu Aug 3 19:56:52 EDT 2000)
n> 2881532+233680 [100+105072/
n> (... hangs indefinitely)

---
Makoto Fujiwara