Definitely the C4 or the aod. Or even the aode. You would probably have to tweak the aod with a higher stall converter and shift kit at the least and you can just reprogram the aode with the stand alone controllers that are available. The C4 has very little parasitic draw on your hp unlike the aod and aode which will suck about 25 hp just for the privelige of overdrive. However, you can run some 4.11 gears for the kick in the butt and shift to overdrive for the equivalent of a 3.00 highway cruising gear above 45. I like it.