I'm getting ready to put 33" on my 06 5.4 and before I do I want to make sure there not gonna kill my trans and engine.

There gonna be on stock 3.73 gears

My combo is gonna be 33x12.50x18

Any insight would be helpful.

 

3.73's will work just fine. That'll be a very descent combo, especially if you're not doing any major towing. Even 3.55's aren't really any trouble with 33's, but it's more noticeable and makes towing less than enjoyable…but you're OK!

 

x2, 33x12.5/20s here, About 100lbs per corner, everything is fine and the truck still moves fast. Lost 1.3mpg.

 

Been running 33's on stock gearing for 3 years now with no problems. I noticed the weight change in the pedal but its all worth it for the function and looks

 

I've got 33s on my 4.2L with stock gears and havent had an issue. Whatever i lost when i added the weight of the larger tires i made up for with a k&n and the gotts mod.