3k is pretty much where I sit with 5.13's with a 3.6 automatic on 37's at 70 mpg. Ive never really felt under powered but also I live in New Jersey so it's pretty flat.
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^^^ Ditto. Except for the NJ part.
aiyadude, based on your last post, you still seem confused on the relationship between tire size and gear ratio, as well as what changing your gears is actually going to accomplish for you.
5.13s for example, are a "lower" gear ratio than 4.88s, even though the number is larger. The reasoning is that the pinion has to turn more times to make the ring gear turn once. That results in greater torque multiplication, higher RPM for a given ground speed, and thus a lower maximum speed. Sometimes you'll hear "low" gears referred to as "slow speed" gears.
Whatever gear ratio you may have, larger tires will raise
the effective gear ratio, which means lower RPM for a given speed, higher maximum speed (if you actually have the horsepower to produce that speed), and less torque multiplication (poorer hill climbing ability).
The standard approach when one adds larger tires is to change to lower gears (numerically higher). This helps an auto trans find the right shift points and maintain the gear selected, keeps your engine operating where it was designed to operate, and because of the additional torque multiplication restores the "drivability" lost to the larger tires. Done right, the gear swap should put your engine RPM at any given speed, back in the same general vicinity it was from the factory (before you added the larger tires).
Your complaint seems to be with drivability, but also with what you believe to be too high an engine RPM. "Drivability" is very subjective and is impacted by many more factors than just tire size and gearing (weight of wheels, weight of tires, rolling resistance of tires whether MT or AT, viscosity of the gear oil in the differentials, ambient temperature, altitude, wind direction, external drag coefficient both inherent and that added by aftermarket accessories, etc., etc.).
IMO your 4.88s might be a little on the "low" side for your undersized "35s," which could give you a bit of an over-revving condition, but it should also give you better
grunt and hill-climbing ability ( although you may have to slow down because of the engine RPMs). Many people run 4.88s with true 37s and are happy with the drivability and RPM. Others prefer 5.13s with 37s for a little extra grunt, but they will elevate the engine RPMs slightly. If you feel that your rig just doesn't have the oomph to get up the hill, then you need to opt for one or a combination of a few things: 1) more power, 2) smaller tires, 3) "lower" gears (numerically higher), 4) lighter weight, 5) decreased drag whether aerodynamically or internally (from fluids, lockout hubs, etc.). If you feel that your rig is already over-revving, then your solution is to go to higher
gears (numerically lower) and/or larger
tires, but I promise you your drivability in hills will suffer from that move.
It may be that you're expecting to maintain an unreasonable speed for the grades that are causing you problems. 3500 in 4th is definitely not excessive (on a grade) and doesn't sound like it's on much of a grade if it will maintain that. If it is on a significant grade, then your only problem is the noise; 3500 RPM in 4th gear for two hours will not hurt a thing as long as your trans fluid is staying cool. And if it's not, you need to slow down. If your horse is lathered, you're pushing him too hard. Slow down to a speed he can maintain. And if that speed is to slow to suit you, then you probably have the wrong horse to begin with.