Yup, 3.9 was original. I have those on the shelf. These other gears are admittedly a bit of an experiment... I was amazed when i found the bearing kit and gears (for GM 55T axle) on justdifferentials.
Not sure about the tires, but I have 32inchers on now.
So far I've found the lugging shifts to be 'tolerable' with the stock cam, but certainly wouldn't want to sacrifice any low end torque from my cam.
The gears & tires really shine on the highway though... I can cruise 65mph with the rest of traffic on the highway & get ~15mpg. Not bad for an ol suburban
