Well I was told I would need gears replaced with my 35's. 20's are alot heavier then 17's and if they are not forged aluminum they are even heavier. I beleive there is only a 10lb difference in tires going to 37's, so I don't expect a noticable power loss. I don't know how much heavier your rims are then mine. With the price of gas and new gears reducing gas milage maybe you should start with the stuff I did if you haven't done so allready. Unless someone knows for shure some kind of damage can occur, then chime in please.

Tru Flow cold air intake
JBA heat coated headers
Diablo Predator tuner
Custom exhaust: y-pipe replaced with X pipe, twin 2.5" pipes to one magnaflow with dual in/dual out pipes then turn downs (don't think turn downs are needed but again everyone thinks so).

 

im thinking on getting 18 inch chrome 18x10 wheels dunno wut kind yet still looking but ya gonna be a 18 inch i dont want a 20 ........

 

I have Weld Racing (forget model but are Forged polished aluminum). They have 18x10's and 18x12's. I was thinking of getting the 18x12's myself and selling the 17x10's but I doubt they would be easy to sell.

 

Goracer, you spent the same amount on those mods as gears would have cost. One way or another, 35" or 37" tires need help in the performance area IMO.

 

I got alot better deal then just gears for the money. I have a faster truck with better gas milage. It's also alot quiter then if I changed the gears. The tuner compensates for the tire size and increases gas milage, the gears suck more gas. The headers and open exhaust makes the truck more efficient, cooler and faster. Gears would make it faster but you still fight restrictive manifold and 2 in to 1 exhaust system. I think the gears should be a last resort and I got alor more for my money as well as better results, then just gears alone.

 

GoRacer, I am on my stock 3.73's and on 37" Mud Grapplers (Sal what do you think yours weigh?). If the packaging was right these weigh around 215lbs each! You significantly reduce your gear ratio going up in tire size so your highway mileage should be great, if you drive a lot around town I'd suggest getting gears. I have intake, exhaust, e-fans, custom tuned XCal2, removed rear cats and had underdrive pullies. My power is great for sitting on 37's, my low end is the only thing hurting. I turn around 1100-1200rpms @ 55mph. @65mph I'm turning over 1600-1700, big difference. Like I said if you do a lot of highway driving you should be fine, the RPM's at 55mph are great for gas mileage. I need to get a video of that.

 

Like I've posted before, Engine load has a big effect on gas not just rpm.significantly heavier and larger tires are harder to turn. Your engine may be spinning at a slower rpm but its also working harder than it would be with the increased help that the gearing would give it. While your rpms go up it is possible for your mpg to get better with gears simply because the engine is not working nearly as hard keeping the larger, heavier tires spinning.