Best gear ratio for towing

[Stroked1]

Question for some of you gearheads.
I have a 1997 F250 4x4 with 7.3ltr powerstroke
I have installed a 8" lift and put on a set of 37" Toyo open country tires. (the truck sits high)
I tow a toyhauler 13k lbs fully loaded.
I think my gear ratio is 3:73 or 4:10's.
I have installed an afe 7pro air intake
4" exhaust, and a ts performace chip, autometer guages
When I tow this thing to the oregon dunes, the truck struggles on just slight hills(exhaust temps in the 12's) (not good)
I plan on installing a 6.0 ltr intercooler.

Question:
Is the truck performing right or do I need a different gear ratio?
Something is just not right.
Any help would be appreciated....
Thanks.

[STurbo90]

on the 7.3, with 37's you would probably want to go to 4.56's.

pre SD 7.3 had either 3.55 or 4.10, all srw SD had the 3.73.

[Stroked1]

Thanks,
But will that do to my mileage?
Can I still do 65-70 mph out on the freeway?

[SmokeyWren]

One of the Toyo Open Country A/T 37" tires has 569 tire revs/mile.

Stock tires on a '97 HD had 655 revs/mile.

655 minus 569 = 86 divided by 655 = 13 percent.

4.10 plus 13 percent = 4.63

So a 4.56 rear axle ratio with the tall tires will get you back to almost stock performance of a 4.10 axle ratio with stock-size tires. It won't get you back to the fuel mileage of stock tires, because of the increased drag of the bigger tire patch on the road, bigger tire crashing through the air, and increased frontal area of the taller truck crashing through the air. But you'll have those regardless of axle ratio. (News flash! You have to pay to play.) [img]/ubbthreads/images/graemlins/eek.gif[/img]

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Can I still do 65-70 mph out on the freeway?

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Sure. With the taller tires combined with the shorter legs of the 4.56, you'll be back to close to stock RPM. With stock tires and 4.10 rear end, 70 MPH was about 2,200 RPM. With the tall tires and 4.56 rear end, you should be less than 2,250 at 70 MPH