There is only one true automatic transmission for the big trucks, Allison. They are a fairly expensive upgrade over the manual transmissions. About 20 grand upgrade for the big one capable of handling 550hp and 1550 ft lbs of torque. There are several automated manual transmissions and they are really catching on. Biggest problem is finding and keeping drivers. Then see if you can find one that can drive a manual trans. Very few of us left. As far as number of gears, five forward gears is the minimum, the most was probably the 20 speed Spicer, heavy haulers and off road users.