Well, I’m no tranny expert but your shifting problem could be the 1-2 solenoid. But most likely you have a burnt clutch. If that is the case a rebuild is in order. Or you could have the line pressure bumped up and the fluid changed, that might mask the problem for a while.

Ignitions on GPs are nearly bullet proof, so yours going bad sounds like a hick mechanic con. Are you misfiring? Also, be aware that it is time for new plugs and wires if they have never been changed.