Anyone noticing MIDI slop with 5.1?

[DaveCarlock]

I've got a session with about 16-20 tracks, a lot of plugs--enough to reshuffle 2 MIX FARMS + a DSP Farm--, & some repetitive plug in automation. I'm noticing that a simple Kick, Snare & Hat track are all over the place from time to time. Single snare hits WAY late, i.e. If I try to replay, it repeats the error sometimes, most time if appears to be a completely random thing. This is completely bad as you can imagine. Is there a pref setting I need to be aware of or something else I can do to get these tracks tight?

G4 350 w/ 300-some RAM.

HELP! This bites!