M2 /w ISC + 3200 - 3.90 too tall ?

[phatbob]

Hi

I've been looking at a "new" (used) M2 with the ISC and an Allsion 3200 (6spd w/ two overdrive gears). Only prob is it's spec'd with 3.90 rear end... running low pro 22.5s (255/70/22.5).

We're in the mountains pulling 18-20,000 lbs trailer... just cars. will it be too low ? By my calcs in 6th we are right at peak torque at 60mps (1400 rpm)... but yeah I know its geared high, but is it too high for longevity ? what about starting / merging up them hills ?

thoughts ?

 

[piper1]

It's a tad tall but not a deal breaker. You just have to get used to it dropping into 5th when you climb a good hill. 5th is still OD and still a locked T-converter so you will be ok, it will give you nice mileage on the flat lands!!

 

[phatbob]

my thinking is we will probably end up in 4th though on the big passes... and/or overheat the trans ?? i guess not if its locked, didn't know when it would/wouldn't lock