My 355 shifter hangs up between 5 and 6

With warm engine and warm oil all around - the shift lever hangs up and requires up to 15 lbs of force to move past the detent between 5 and 6. This started occuring just after my 30K, but the dealer assures me the only thing he replaced was the flywheel, clutch and pressure plate and related bearings. He says he didn't touch the inside of the transmission. I've tried different lateral positioning in the gate to see if that has an effect, but it doesn't seem to. All other gears are smooth even with cold oil. Is it possible a bolt or shroud is hanging up as a result of re-hooking up the linkage? Every thing looks normal from underneath.