Hi,
Got a 97 venge 5spd with 85k on it, never really had any problems with it until last week. I was driving put it in third gear and it popped back into neutral a second later. I thought I might just have nicked it in with my hand so I put it back in and drove around in third for a bit. It stayed in no problem up until about about 4500rpm and popped back out. This only happened  in third gear.

I've been driving it for the last couple days with no problems in third gear for the last five days.....I even got it up to 4K rpm or so which is as high as I wanted it to go. THen as I'm cruising home I shift it it to fifth and it pops out of fifth!!!!! Put it back in holds for like a sec. and pops out.......

Got home pulled the center console to check out the shifter and I really torqued down the two bolts that hold the shifter lever in place so there is much less freeplay in the assembly itself. Took it back out for a couple mile ride, went through all the gears, and no problems at all.

I've noticed that the 4 times this has happended just a second or two after shifting in to the respective gear. I have no grinding or notchiness and the car shifts smooth as butter in every gear.

Got any ideas? I checked in my Haynes manual on how to adjust the shifter but it is completly useless for that.

....I know nothing about manual trannies except I wanna get wanna soon...sorry I couldnt be of much help..but like tengu said, since your tranny seems to be going..aka ur clutch, I guess you dont have a choice but to check that...or as nykon would say...check your fluid. lol

LOL MX3 doing 120, that just sounds funny.  I had a buddy that had one, it looks like a cumbubble.  Not saying it didn't happen just pictuing my buddies all white sperm swimming at 120

lol yeah we did a bunch of mods, it'll do over 150 mph now ... limited by the tranny it climbes as fast from 0-60 as it does from 60-120 it's quite a mean machine.  We had to remove the speed limiter though haha (screw 4A if i remember correctly in the back of the speedometer for those mx3 users, just remove it)