The Hemi's have a different tranny. Ours are very slightly modified diesel trannys. They are almost purely mechanical. The computer can modify governor pressure which can make it shift. The computer can engage and disengage overdrive (4th gear), and the computer can lock/unlock the TC. That's it. The computer cannot control line pressure or anything else. It cannot control shift firmness. It only controls shift timing by tricking the valve body. It does this by holding the governor pressure low until it (the computer) wants the tranny to shift. It then raises the governor pressure and the valve body shifts the tranny. The computer watches for the sudden rpm change to know the the tranny shifted. It also compares the input speed to the output speed (engine rpm vs. output shaft speed) to estimate what gear it thinks the tranny is in. It then adjusts the governor pressure to where it thinks it should be, based on the speed you are going, so that the tranny stays in the proper gear. There are no sensors or anything in the tranny to tell the computer what gear the tranny is in; the computer must make an assumption. On the diesel trannys, the computer can pull or relax the throttle valve (TV) to change the shift behavior depending on whether the turbo has spooled up or not for a given throttle depression. Ours are a mechanical cable connected to the throttle body.
It is really an overly elaborate way of wrapping a control system around a purely mechanical transmission and getting it to behave like an electronically controlled tranny. It works fine as long as the tranny has no problems and is operating within known parameters. Incidentally, that is why you have to keep everything adjusted just right (2nd gear band, TV cable, fluid level, etc) or the tranny will shift funny. Once it gets out of whack, the computer wrongly assumes which gear the tranny is in and doesn't command the proper governor pressure, and it starts that 1-2, 1-2, 1-2 crap or it does not raise the governor pressure high enough and you hit the rev limiter before it shifts, etc.
Sometimes our transmissions shift too soft, and other times they shift too hard. Since the computer cannot control the shift quality or firmness, the mechanical valve body is just reacting based on its internal spring pressures vs the myriad of fluid pressures against various shift control valves, accumulators, and shuttle valves. All of this will will fluctuate with fluid temperature and the amount of moisture dissolved in the tranny fluid (which can affect how grippy the fluid is at the moment) and the condition of the clutch packs and bands.
Our trannys can be made very strong and durable and can shift hard enough to break the drive shaft, but it's difficult make them shift hard when they should and shift soft when just tooling around town, without adding a bunch more electronics -- which our trannys do not have. So, you either have a weak tranny, or an axle snapper. That's why everybody hates these trannys.
Mine is leaning toward the axle snapping side. It is entertaining, but a little obnoxious.
