89 chevy k1500 4×4 only 68,000 on motor and tranny wont go into reverse or drive... wont move.... whats wrong with it? Did my rear end maybe go out?

Inspect the linkage to the trans, it may be bound or broke.

Check the transmission fluid for the proper level. Not knowing your driving habits or where you have been driving the truck, it is possible you have debris in the linkage, bent the linkage bars or it is just tired and gone out of adjustment and needs new parts to refreshen it.