Which transmission?

I'd look for 3.55s and an 18.

 

18spd/3.25 rears just my $0.02

 

13 and 3.55's/3.58's.there are times that 18 is just too much shifting especially if driving in the northeast.
heck,3.70's may prove more efficient up that way.

 

With that kind of weight a 13 or 18 would be helpful when getting off the line. If it's "to much shifting" when you light you can always shift it like a 9 or 13 speed and skip the splits. Honestly on hills, I love my 13.

Fl columbia will get a mpg better then a 379 at highway speeds.

 

How can anyone possibly recommend rear end ratios/tire size without knowing road speed or the engine under the hood?

 

for rear end, you need to know planned cruise speed and cruse rpm as well as tire size. I think they were recommending average specked engine. Although, detroit and cat cruse at different rpms so it would be nice to know.

 

surelly tranny with splitter. 18 st fuller ore ZF16

 

BTW, I can see no reason for autoshift

 

Real good set up.