BurbMan wrote:
The downside is that they are programmed to upshift and run in the highest gear at all times to maximize fuel economy. Anytime you hit a slight incline or need a smidge more power, you cause a downshift. Seems like the more gears you have the harder the trans works, the PCM is constantly shifting it, either up when you let off the gas, or down if you step on it even a little.
Yeah, it depends on the truck, but I have to wonder at what point do they think an engine can push 4 OD gears in real-world scenarios, even driving unloaded.
The 6 spd in our '10 Suburban (2 gears above 1:1) does pretty well holding the gear above 70 mph, but of course it will have to shift down on a moderate grade. At 65 mph and below, however, the engine isn't turning enough rpms to generate power -- it is at about 1700 rpm at 65 -- and it downshifts from 6th on the slightest incline.
The 6 spd in our '06 Duramax (also a double OD) was perfect for that engine, with the engine making peak torque at 1600 rpms or so -- it could hold top gear up any Interstate grade I encountered, as long as you could keep speeds above 60 mph or so to enable the engine to operate at its torque peak. Heck, it could keep 6th gear up most grades you find on the Interstate even when towing as long as you could keep the speed up.
