you should get your money back and back charge them, my mates TX3 has had ALOT of issues too, he ended up going to a dog engagement PAR, his car is only used for drag racing but,
he had heaps of synchro issues too,
the PAR dog box has copped alot of abuse and has even gone back into 1st gear twice during 2 different drag runs (NOT GOOD)killed his motor the 2nd time and broke a driveshaft the 1st time.