Just bought a 1994 Sierra extended cab with a 383 Stroker in it (350 4L60-E tranny) and the transmission doesn't shift into third. I don't know what the problem is (before you ask, I was aware of that issue when buying the truck), it could be the 2-3 shift solenoid, clutch issue, linkage, etc. The shifter is pretty loose, I don't know if that matters or not linkage wise. It's sort of limp if that makes sense. 1st and 2nd still work great, so does reverse and 4WD, but it doesn't shift up into third.