Are you talking about regearing or keeping the 3.55s in the axles? I know keeping the 3.55s are bad for 37s but I'm on the fence about 4.10s or 4.56. Because My truck with previous tires which exact are 32.5 I think they are just 1.5" bigger than stock and I never hit 2000 rpms until i was going almost a 100. I wish it was at 2000 rpms at 75. I've always had so many issues with the truck keeping its speed down the interstate. Idk if all 2nd gens like mine have this issue but my O/D in my truck was useless on the interstate going 70 or up no matter the rpm it would not keep or gain speed unless it down shifted to a lower gear and was roaring down the interstate at 3500 or 4000 rpms. Or if it was going down hill or on flat ground so idk if I need to gear higher for it to be equaled out? Sorry if i sound confusing but I felt the truck needed to be regeared badly with those 32.5s. The truck has had the issue since we bought it back in 2002.

 

That is just how they operate. Mine is slightly better with 4.88s and 40in tires

 

Your truck should be able to maintain speed on reasonable hills, even in O/D. Think I would start looking at the plenum, tune up parts, and things of that nature.

 

I would run 4.56 or 4.88. Your adding a lot of rotating weight and raising the truck which kills aerodynamics. Your fuel MPG is going to drop. Here is a gear calculator https://www.rocky-road.com/calculator.html

Personally I'd lean to 4.88 or 5.13 with a 318 and not run over 70. Honestly we need more information to help you select gears. What driving conditions are you using the truck for most of the time? To and from work ? What speeds? Do you live in a city with lots of traffic? Will you tow a trailer frequently, occasionally, never? How heavy if you do? Is your drive to work 5 miles, 10, 20, or 50 miles? In town or on the interstate? Any off roading?

You need to gear for what the truck will do most of the time and make trade offs for things you don't do often. If your stopping and going in town mostly, a lower gear like the 5.13 or 4.88 is better. Mostly interstate use the 4.56 or 4.88. Be honest so you get the best result.

 

I think he is talking about the shift patterns
Highest you can go for a Chrysler 9.25 is 4.88

 

+1 The first performance degradation, with any vehicle, I typically notice is highway performance with overdrive. The indicator is the transmission won't stay in overdrive on even light hills. I usually start with a fuel system cleaner, and if that doesn't fix it, progress to cleaning/replacing sensors and tune up parts. You should probably do that stuff first so you establish a good baseline.

 

Alright so we own a custom cabinet shop that is at the house so I literally walk to work every day. We have a duramax we use for pulling most of our big trailers but every once in a blue moon my dodge pulls a enclosed trailer full of cabinets. Most of the time I'm only pulling ATVs to mud parks which is like once a month so I dont pull a whole lot of heavy stuff. That being said my truck is really only drove on the weekend to and from my girlfriends house which is 40 mins away on mostly interstate. I hardly offroad since most of the truck is in brand new condition. I live near a moderate sized town. No heavy traffic. Most of my riding consists of highway and back country roads. Its my daily I guess youd say cause it's the only truck I have that's 100% reliable. Like I said before I drove it to Florida 400 miles away one time. And as tunning up what do you mean by that? As of now I dont think there is much tuning left on my trans or engine. I cleaned the injectors, new spark plugs 30,xxx miles ago, new throttle sensor, new air intake, has a programmer on it, has high performance exhaust including headers, has a rebuilt trans, and brand new cooling system with radiator. Only thing on the engine that has issues is the freeze plug leaks and valve covers leaks a little. Is there anything else I should before swapping the gears or check?

 

the gear calculator you suggest said I need a 4.23. So I'm starting to lean more toward the 4.10. Idk if this makes much of a differnece with regearing but the truck has a 2500 suspension, steel offroad bumpers, standard size tool box, and 18x10 rims instead of factory. So with all that added weight I'd guess youd stt my truck isnt really a 1/2 ton but not a 3/4 ton either and I know the weight effects all of this.

 

You should check the plenum, and did you replace the distributor cap and rotor? You could also clean the throttle body and the sensors that plug into it. If the cats are still on it, make sure they are not restrictive.

For comparison, when Dodge added 33s as an upgrade (275 60 20) on their 1/2 tons - they required the rear gear be upgraded from 3.55s to 3.92s. I'm running the same tire with 4.10s, and if I wanted to go 10% taller tire (33 -> 36.3) I'd likely go 10% more gear (4.10s -> 4.5s). Seems like 4.56 would get you back to stock RPM ranges if you used a 37" tire. I think if you want to retain truck capability, 4.56s are the way to go.

Are you running 8 bolt axles (aka d60/70/80?) ? If you are, you would need to also replace your limited slip case - they sell those in 4.10s down and 4.56 up. Can't move from 4.10s to 4.56 without that change. I don't know what the caveats are on 1/2 ton axles, there may or may not be issues as you move to the more extreme gear ratios.

 

You have D60's under it??