Attempted to launch my car 96 coupe with gsr swap last night and it poped out of first gear. Every time I lauch it pops out and at lows rpms same thing. Tranny was rebuilt less than 5000 miles ago. Any one have an idea what it could be before I rip it out again?

 

bad syncro retainer the syncro retainer will hold the gear in 1st gear and if it is broken or damaged it will not hold in gear .

 

The retainer might have been bent when it was rebuilt if the person who rebuilt it wasn't paying attention. I've done that before. You'll have to tear it down and replace it. Someone on here should have one lying around since you can't buy it seperately from the gearset (not OEM at least).