1999 Pontiac Montana Hard shifting and shaking on takeoff

It's shifting hard getting to shift to 2nd (like slipping), but higher gears seem to work fine, highway seemed ok. But on takeoff it has now sometimes started really jerking and shaking. This is weird because it seems to happen more as the engine heats up. Works better cold with less hesistation going into 2nd when first started up and going. It seems like a similar problem I've had before and I took it to a tranny shop (expecting the worst) and they swapped a fuse in the engine compartment and it was all better. I hope it might be that fuse again, however a fuse is bad or it isnt, not intermittent or worse as it heats up. Anyone know what fuse they might have changed before (so I can change it. Will m ake me feel better anyway) or something else to try and resolve this?

*edit* Since I forgot to put it already, yes the engine light is on, has been intermittently on for like a year. I am actually going to buy a reader so I can see what the codes are that it throws up all the time. Also the shifting problem is apparently a progressive thing, my wife says its been doing here and there some for a while now(thanks for telling me now when it's going all crazy on New Years Eve) but getting worse now, and again, develops when it heats up, not so much when it's cold.