No I didnt up grade to 3/4 ton axles still have dana 44 and Chrysler 9.25 but like my leafs in the back are off of a 2500 truck and the coils and such

 

Your 37" tires are probably shorter so I used 36. 2174@70 and 2330@75 with 4.56. We have 4.56 with 33s in my daughter's truck. If she ran a lot of interstate we'd put 35s on it. I think 4:56 would be close to matching the stock ratio. Someone correct me if I'm wrong on the trans ratio in overdrive.

 

O/D ratio is .69.

 

Don't get 4.10s not enough gear for 37s. I would go with the 4.88s. More rpms doesn't always mean less fuel mileage, you engine and transmission wouln't have to work as hard with 4.88s.

 

4.88s I think are a little big for 37s I'm running 4.88 with 40in tires and they put me right back into the factory RPM range.

 

You want to be higher than the factory rpm range because the bigger tires are heavier and have more rolling resistance.

 

I mean I'm close to factory range if it had bigger tires. I used a gear calculator and even talked to a shop and they recommended that size. It does have more low end getting because if the higher gears.

 

To my knowledge 4.88 gears is the lowest you can get for a Chrysler 9.25 so that was probably why they where recommend because you can't get any lower.

 

I'm running 4.88 in my 2500 HD and my 1500 with 40in tires

 

This.

That's the steepest they get for the 9.25 axle.