it dont want to backup,acts like its going to tear the rear end out. on 1995 GMC Jimmy

checked transmission fluid, and goes fine forward

Asked by for the 1995 GMC Jimmy
you have an internal trans failure. you will need a trans shop to remove it, identify the issue and re build the unit.

1 more answer
You'll want to visit a reputable transmission shop for a test drive and diagnosis. Its sounds like and obvious driveline issue.