gear ratio questions

[fightinfire03]

i have a 2004 250 4x4 that's on 38s. i bought it used, and the previous owner lifted it and put bigger tires on but did not mess with gear ratio. it's not a huge deal i know the truck can handle it, i just don't like the idea of sacrificing the power bc i think going from stock tires to 38s is significant...i plan on getting a programmer in the near future, but still want to look into correcting the gear ratio. anyone know any good sites or have any good experiences that could help me out? i'm not much of a 'just drop it off at the shop and let me know when it's done' guy. btw, the speedometer is off by about 9-10 mph, judging by what it reads vs. what my GPS says i'm doing. seems like after the fix, if done correctly, the speedometer should be pretty close if not dead on.

[PGreenSVT]

Depends what you do with the truck which gears you go with. Either 4.30's or 4.56's. Personally I'd go with 4.30's but if you tow heavy 4.56's would be a better bet.