I've got a 1992 chevy 2500 4x4 6.5TD/4L80E 3.42 gear The trans shifts great in all forward gears, no codes, and locks up the torque converter as it should. no slipping whatsoever. When put in reverse it clunks like its engaging, then won't move, no sign of moving. It clunks like its in, but 100% freewheels. Any chance its something stupid and easy??