HELP (transmission doesn't shift)
 

I was stopping at a stoplight and it "clunked" as if I'd killed the engine but the engine was still running, and now can't get into any gear except 5th or reverse.

any help or ideas would be greatly appreciated

Truck Info (incase it's pertainant) it's a '90 F1504x4 with 5spd and the 4.9L engine, it's had a 6" Rough Country lift and has 33x12.50 Peerless Wildcat EXT's on it.