37s on stock 3.55 gears and it is a dog, is regearing to 4.88 worth the money

the math first because it settles most of the argument. to find the gear that puts you back where the factory had you, take your new tire diameter over your old, times your stock ratio. you were on 33s, now on 37s. 37 over 33 is about 1.12, times 3.55 is 3.98, so a 4.10 would put you exactly back to stock feel. there is no 4.10 option for your axle, so you round up to the next real ratio, which is 4.56 or 4.88.

4.56 gets you a hair past stock and keeps your highway rpm reasonable. 4.88 gets you a little more than stock, which is what most people on a 37 want because they also tow or climb, and your 10 speed has enough ratios up top that the mileage hit at highway speed is small. i would not go 5.13 on a half ton EcoBoost that you daily, that is a rock crawler gear and you will be at higher rpm on the interstate for no reason. for Pueblo and the grades, 4.88 is the one i would do.

and gear both axles, always, you cannot run two different ratios front and rear. budget a locker or a limited slip in the rear while the diff is apart, because the labor is already paid for at that point.

diesel so my numbers do not map to your EcoBoost exactly, but the cost side will. i regeared my 2500 from 3.42 to 4.10 for 37s. ring and pinion sets were about 350 a pair, a shop i trust charged 1,100 labor to do both axles and set them up with the bearing kits, and i added a rear locker for another 650 installed since it was open. so i was all in around 2,400 with the locker, closer to 1,800 without.

the thing nobody warns you about, a gear setup done wrong howls, and a howling diff on the highway will make you want to drive it off a bridge. pay a real gear shop, not the cheapest guy, because setting pinion depth and backlash is a skill and a sloppy setup fails early. i watched a buddy do his twice.

i am the cautionary tale. i run 35s and i kept telling myself i did not need to regear because 35s are only a little taller. i was wrong, the 5.3 with the stock 3.42 on 35s was miserable, and i finally did 3.73 which was not enough and i should have gone 4.10. do not half measure this. if dale's math says 4.88 for your 37s, do 4.88, do not talk yourself into 4.56 to save highway rpm and then wish you had more.

and get the speedo recalibrated when you regear, because a tune or a programmer has to tell the truck the new ratio and the new tire size or your speedometer and your shift points are both lying to you. there is a whole thread on the recal if you need it.

reading this because i am the next step down the ladder, 33s on a level, and even that little bit made my speedo read 3 mph slow and knocked my shift points off. for a 33 on stock gears a recal is enough and you do not need to regear, but your 37s are a different planet and i am glad the thread talked you into the gears and not just a tune.

for anybody on the fence at a 35 or 37, a programmer can correct the speedometer for the tire size but it cannot give you back the torque multiplication a taller tire took away. only gears do that. the tune fixes the lie, the gears fix the truck.

good outcome and a clean set of real numbers, which is what this board is for. for the searchers, the short version. take new tire diameter over old, times stock ratio, round up to the next real gear. that is your answer, not a slogan. on a 37 off 33s that is a 4.88 for most half tons, and you gear both axles or you gear neither.

one part spec worth knowing while you shop, if you want a tire that holds its real diameter and does not grow at speed, look at the load range and the build of the 37 itself, a cheap soft sidewall tire reads a different rolling diameter loaded than it does on the rack. plenty of real options out there, one example people run is the nittotire.com Ridge Grappler in a 37, but the point is pick the gear for the measured diameter, not the number on the sidewall. marking this solved.