I have posted various questions on this - but this should be my last one (hopefully!). My 97 Dodge Ram 2500 xcab long box 4x4 has 4.10's, auto and 265's. Since I bought it in April I have averaged around 15.5 mpg overall. Here is a breakdown:

Empty driving to/from work at 65-70 - Approx. 16 mpg
Empty driving all highway at 70 - Approx. 18 mpg
Loaded with slide in camper (1600 pounds) and towing Jeep on Trailer (approx. 6000 pounds) driving 65 - Approx. 12 mpg

I have working on collecting parts and info on swapping to 3.55's. I bought the . Here is a breakdown:

Front Dana 60 3.55's for $60 shipped (used stock gears)
Rear Dana 70 3.55's for $80 shipped (used stock gears)
Full install kits for both axles shipped - $325
Installation - I found a guy willing to let me help and learn so deeply discounted - $250
Total cost - $715
Sell 4.10's - $200?
Final cost - $515 ish

Any idea how much better my mileage should be after the swap? I am hoping for 3 mpg better (18.5 mpg average overall?) - is that realistic? Here is what I computed:

Diesel @ $3.10/gallon at 15.5 mpg = $.20/mile
Diesel @ 3.10/gallon at 18.5 mpg = $.1676/mile
Difference in cost/mile = $.0324
Cost of approx. $550/.0324 = approx. 17,000 miles to make up the cost.

Are there any other benefits or disadvantages to making the swap? Do you think it is worth it or would my money be better spent on other mods to get better mileage? Thanks for you input!

 

Well, it depends on how you drive. I feel like 4.10s are overkill unless you tow very heavy all the time and don't mind the lower fuel mileage and higher revving at highway speeds.

If you have a 5spd it is a bit worse than with an automatic, because the final ratio on the 5spd is a bit lower than that of the auto.

I have 3.54s in my dually... I like them a lot more than the 4.10s in the 2500 (both trucks are '96 automatics).

Its up to you, but I think it would be worth the cost JUST for the better driveability.

 

I have the 3.55's and have averaged 19-20 mpg. since new highway drivin'.

 

My best hwy is 19.8 I probably average around 18.5 hwy. I would like the 4.10 for towing in the mountains but I am leaning towards a us gear under drive for the best of both worlds!

 

I did it to a 3500 and LOVED IT! i hated thoes 4:10's
I wish they had a like......3:68 gear. that would be nice.

 

well if anyone has a dually with 3.55's and wants 4.10's, in Washington... Let's swap!!! lol

 

i have the 410's. i get right at 20 mpg hwy. pullin our 5vr we avg about 10.75 mpg w/a 17k gcvwr. thats avg mpg over a long trip. Looks like your at about 15k. don't know if the 355's will give you better mpg towing, but it will unloaded. we do a lot of colorado, nothern NM, smoky mtns. i'm keepping mine because i like the power. it's also less strain on the tranny. i read a post here bout someone gettin better milage w/ the 355 to 410 swap towin. my owners manual rates the 3/4 and 1 ton gcvwr for auto and manual @ 16k w/355's and 18k w/410's. if i didn't tow, i'd have the 355's, but then, i wouldn't have a diesel truck.

john
95 slt w/237k, custom leathers, auto, cc, lb, 235/85 bfg commercials, 410's, kdp tabbed, KnN, timin advanced, grnd stock plate, more boost, hvy duty tranny, billet tc, tc lockup sw.