The problem with the t56 is the truck would be useless as a tow vehicle. I figure with the stock diameter tires and 2.73 gears in the rear, 70 mph in 6th (.76) gear would be 1,600 rpm and with 3.08 gears, 1800rpm. With 2.73 gears 2nd gear would still be useable as a starting gear on the street. But when it comes to having a little fun 1st gear at 1000rpm is about 5mph. The z51 packaged corvette goes 7.87 mph at 1000rpm with its stock rear end. Changing it to 4.10 gears is 6.56mph at 1000rpm.

I guess this transmission is a little to wide ratio. I just which there is geared in between the t56 and the zf that can take the power of 500 - 600 horses and not have a problem towing 5000 pounds when needed.

About the size of this transmission, everybody seems to think that this thing will be touching the ground. I guess I have not actually seen one of these things in person but looking at the transmission on this webpage http://www.thedieselpage.com/duramax/ZFS-650.htm it seems to me that the transmission doesn't fall but a couple of inches below the bottom of the bell housing. So, wouldn't that mean if the transmission was touching the ground, the oil pan on the engine should be too?

Anyway I am still evaluating my options and who knows by the time I actually get the money to get this far on my truck (2 years down the road), I will have some other tranny option to deal with. Maybe for now a tko would be a better option to solve my problems. The goal for this discussion for me was to figure out what I need to do so I am not purchasing extra services for something I am going to pull out later.

Thanks for the input