timing on stock trans
 

My 98 12v cummins I bought 2 weeks ago has turned into my daily driver. I am getting 18.7 mpg the truck is all stock with 3.55 gears and the auto trans. my question is if i advance the timing to get better mpg how will the trans hold up? I do not do any pulling with it and only run the speed limit. I called suncoast about a trans and it is 4500.00 dont have the money right now but maybe by next year. the truck has a reman jasper trans with about 17k miles. any input????

if you take it easy i think tranny would be fine.