Well hmm, does your system behave when autofs and nis+ load at boot?
I wonder if something is taking too long to load, making nfs die. This sounds like what happened when I would LAN at my friend's house. I had in my fstab an nfs line that would stall my system. I ended up going into runlevel 1 and commenting it out. But that was after waiting over 30 minutes for it to stall (which it did not, I 3 finger saluted it to RL 6).