new rig.......couple questions
 

i just bought a 96 with 117k miles and a new trans, and was wondering if it would be okay to run synthetic in my trans? does any recomend it? also will going to 3:55 gears hurt my trans or cause any excess wear? im sick of 4:10s and shitty gas milege

i know that that trans requires dextron3 +4 trans fluid. if you find a synthetic equivalant you should be fine.

where you located? ive got a d70 with 3.54's ide sell ya right

synthetic fluid will be glad to absorb the ocasional unintentional abuse we all give our trucks from time to time, i.e. hauling incorrectly or too heavy.. rollin a bit to much coal... etc., im a big fan of running synthetic fluids in place of mechincs in a bottle
I work on alot of cummins and i see the long term effects of lack of maint.
with that being said
long term running synthetic trans fluid seems to be a waste of cash unless you haul and I think your money would be better served on a good aux cooler

just get bigger tires to fix your gearing problem.