the shift forks are also weak in these transmissions. They were aluminum and if you tried an enthusiastic shift, its possible you bent it. This would prevent the tranny from meshing properly. The rebuild kits they offer for these trannys are reasonable but if you're not mechanically inclined then you're looking at around $3k to remove and replace and rebuild the unit you have. You should however at least machine the flywheel, install new bolts and replace the clutch while you're at it AND add a bleeder for the system if your car is not equipped with one. By the time I was done with mine, I think it was around $4k but with the new synchros and steel shift forks I'd say you're good for at least 550hp. In fact with the exception of the output shaft, after you've upgraded the synchros and shift forks, you're pretty much running a viper tranny with the exception of different gear ratios. I would also recommend new gears though and upgrade to the C5 Z06 ratios which are much closer and have only one real overdrive gear rather than the ones you're running.
Just my $0.02