Weird, I don't have any issues like that with my trans and Spec 3 I got from them. My friend however had a weird problem for a while where his Spec 2 would slip in every gear but 4th. We just couldn't get 4th to slip no matter what RPM/load, etc. Now all gears work fine. We had bought a used clutch and used his stock pressure plate and flywheel without getting either cut (yes...I know...stupid, but he was broke, and we had to take the transmission out to swap it with mine anyways). I think his stock pressure plate/flywheel were glazed over from his old clutch slipping so bad (every gear, almost any throttle) that even the light sandpaper we used didn't take it off. Once the glaze wore off, the clutch grabbed everywhere.
This was on an LT1, but still with a T-56 obviously.