ok so i finally found out what gears i have . when i bought the truck it had 39.5/13.50/16 on it and the gears are 4.88. now i went and bought new tires and went down to 35/13.50/16 open countrys . my quistion is what gears should i put in it to run about 1900 rpm @ 65mph. iv tried all the calculatorsand there telling me 3.73 ,3.93, and 3.05 . i dont think there is a differince between these so thats why im asking all you truck pros . the truck is a f250 7.3 diesel auto trans, 6" lift.i have a diablo predator tuner can you adjust the shift pionts with it or can you just adjust the hp and shift firmness. thanks again you guys helped me a ton already and im greatfull.also what rearend do i have or how can i find out , it has a 12 bolt cover, but i dont know if its a 10.25 or 9.75

 

going to 4.34:1 (4.30 is close enough) will get you to the same ratio as where you were with the 39.5's and 4.88's.

to get back to stock gearing, you would need 4.14:1 (4.10 is close enough). at 60mph and stock gearing, my rpm's are right around 1750. so therefore, you should invest in 4.30's. they are a little shorter than stock 31.5''/3.73 (less top end, less MPG on the highway, but easier acceleration) and will put you right around 1850-1900rpm at 60mph. good luck.

the stock rear end is a Sterling (i believe that is the name) 10.25 inch. stock front is dana60.

 

Not quite right there hoss - the OBS trucks were Sterling 10.25 rear axels - from 99-up - they have Sterling 10.5's

Also the front axel could be a Dana 50 - it escapes my memory when they switched from the 50 to the 60 - I think it was some time in 2001, though I could be wrong. I do know that the first Superduties had the Dana 50's

 

duh, sorry. this is from the FAQ-

Q: What kind of axle do I have?

??? A: SRW Super Duty's from '99-'01 wear a Dana 50 in the front (4x4 only). The Dually's wear a Dana 60. In '02 the front axle was changed to a Dana 60 for ALL Super Duty's (SRW & DRW). All SRW trucks use a Sterling 10.5" full floating axle in the rear. Dually's use a Dana 80.

 

I just talked to my local shop about changing gears- 2000 f250 3.73 ls (4x4) Dana 50 up front. He said it might be tough to get the 4.30 for that front end, since it is a dana 60 housing with a dana 44 housing (Or something like that). Have you had any experience with this? I am going to 35's and would like a little better off the line that the stock 3.73's with stock tires. Also, what type of Limited Slip/Locker will work for the 10.5 and the Dana 50? I am not interested in a Detroit Locker and can't bring myself to buy an ARB. I don't do enough off road to warrant the price.

BTW Ford wants $1900 to change to 4.10's with the stock Trac-Lock.

 

Sure you can. Up too 2001, the V10 SD Lariet came with 430s.