Last week I replaced the pinion seal on my 1999, F250, 5.4L SD truck and was advised there was slack in my pinion gear which could cause the seal to leak again. If this does happen and I am faced with replacing a pinion gear should I consider a gear change for better gas mileage? I presently have a 4:10 gear. I have not had this truck very long but recently calculated gas mileage at 13.9 mpg. Would a gear change to 3:73 help? I have an automatic transmission. I do not tow. This truck is mainly for transportation to work, etc.

 

3.55 might be better for fuel economy...and still have enough to go down the road...

I know a diesel guy that went from 3.73 tp 3.08, picked up about 3mpg...