Im currently running 295 70 17 on stock f150 rims but the center tread is wearing way to quickly so Im looking at purchasing a wider 17" rim. With the 3" level what backspacing would be best to run with no or little to no rubbing? Im thinking a 17x10 or 17x9 rim.

 

Stick with a 17x9 rim and you will not have any issues running a rim with a backspace from 5" to 6". Are you sure it's the current rim width wearing your tires and not over inflation ?

 

I agree.

 

i got them inflated to 40psi im assuming thats not to high for these tires

 

No, it's not high. I wouldn't go much lower.
I'd go with an 8.5 or 9 inch wheel with at least 5 inches of BS.

 

Actually, 40 is too low for those tires. They have a rating of 3195 at 80 psi. Your axles are rated close to 4k, which means your tires need to support 2k each. Your are in total at least 800 lbs short at 40. Even unloaded, the front is probably close to or over that weight. Your biggest problem is rim width.