I did the Transgo TFOD-HD2 kit in my dodge (A518 trans) and there are some parts of the kit that can't be installed without taking it out and apart, but you can get improvements just doing the work on the valve body. There are some holes that get drilled out on the separator plates that control how hard it shifts, a lot of the modern transmissions were built to shift really smoothly, which is done by overlapping the gear changes.. yes, it makes them shift smooth, but it also causes a lot of wear since one gear hasn't disengaged before the next one starts engaging.. the kit should give you the necessary hole sizes to accomplish what you want as well as replacement springs for the ones that often break or need to be stronger (to release a clutch faster).
In your case, it could be a bad pressure sensor, bad solenoids, connections, etc that make it behave poorly as well and a good code read first is pretty much imperative.
If you're mechanically inclined and have (or are willing to buy) a couple specialty tools, (and have a backup vehicle), it's not rocket science to refresh the transmission with new bands and clutches.. I just did a 47RH, really took my time with it, cost me about $400.. replacing the torque converter is a good idea, which is one of the expensive parts of doing it though