pulling hills/mountains

Anything can be made to work,I think it would depend on just how much time you spend climbing hills. I would suspect if pulling is a major problem, I would suggest a lower geared rear. Possibly a 3.70, or even lower if you stay in the mountains. Tire size also contribute to pulling ability, but engine HP is the greatest concern.

There is [ was ? ] a direct 10 speed, but I think now most are OD.

 

i personally would stay away from this one. 3.25 gears are way too high for the hills, especially with a 10 speed. would swapping the rears be an option in the near future? And how fast do you wanna run when not in the hills?

 

i am not a fan of 10spd for the coast..We run 13spd only..I think the 3:55 would be far easier on clutch wear and driver too..

 

10 spd direct or OD?

Just seems like an odd combo for either tranny to be at 3.25.

 

It really comes down to physics. The lower geared rear end, "3.70", is always going to handle the hills better than the higher geared rear end, "3.25". A 3.55 rear with an overdrive 13 or 18 is the best middle of the road setup in my opinion, especially for a cat engine. I guess the question you need to ask yourself is what percentage of you driving is going to be done in the mountains. Over 50% and I would go with the lower gear ratio. Just remember no matter the ratio, if you go with the c15 cat, that engine wants to run at the lower rpm range. The lower you keep your rpms the better it will perform.

 

I has 3.23s with a 550 Cat and a 9 speed transmission. It was a real pain in the butt in the mountains. I took my time and keep dreaming of a 13 speed for Christmas.

 

your thinking is way off on this. No matter what your transmission, rear end, or engine is when you climb hills you downshift until you find that happy gear that gets you to the top running 1400-1500 rpm. If you have 3.25 rear ends it may be 6th, whereas with 3.70 rear ends it may be 7th. If you have a 13 speed it may be 9th, but with a 10 speed it may be 7th. You hear what I'm saying ? You can achieve basically the same ratio of rpm's of the engine vs. rpm's of the wheels with any of these combinations.

And if you are really pulling serious hills with serious loads, your limit is not going to be engine power but cooling capacity. Sometimes you cannot safely use all of the engine. Nowadays they are mostly idiot-proofed but if you have any kind of performance mod's or are hauling extra heavy loads you are often better off to drop a gear or two below what your engine will do and just hold her happy at 1400-1500 and crawl to the top.