Hmmm, this is an oldie but baddie. Most often it is not the transmission. . .
All you should need to do is change the fluid and filter for the tranny. The shifting hard is due to a variety of ECU engine issues. Anyone in doubt, disconnect your MAF connector and drive it around for 5 minutes. I would run the damnation venue out of it for an afternoon and see what buckles under the stress. Now by this I mean drive it like you stole it, not try and do burnouts till your running on aluminum. If no dummy lights then I would go after it 1 by 1. Air(easiest), Fuel, Spark, Grounds and so on. I have seen this caused by the mix being too lean, plugs being shot and a few other issues. Your plugs will tell you a wealth of information about your engine. I wanted to use this principle on my ex-wife to see what was wrong with her, my attorney advised against it.