Have a 94 jimmy,4.3, just bought few months ago,
When its cool, take off runs & shifts fine, couple miles, tranny don't shift right, no slipping, so maybe electrical ? Thanks for any help

 

"Tranny don't shift right" is only useful to a Psychic! First thing you need to do is get to Autozone or some other place that will read the codes for you and report back here with what they are. We also need a detailed description of how it is shifting/not shifting, harsh shift, flaring during the shift, etc. With that we might be able to steer you towards a solution.