with my 4x4 it has 4 cats. will i have to replace all 4 with hi flow or is there a set up to only use 2?

 

Most guys replace 4 with 2, getting rid of the pre-cats.

 

with that being said would i lose any backpressure. causing my exhaust to pop?

 

You can replace your 4 factory ones wiht 2 aftermarket ones, the ones that are reccomended are Magnaflow hi flo cats and you cant get them off ebay for 56 bucks a piece + free shipping.

 

then grab 2 MIL eliminators for the secondary O2 sensors, or the main?

 

You can leave all of your O2 sensors in place. One set befre the cats, one set after.

 

with the hi flo cats it wont cause the check engine light to come on or some kind of miscommunication between the engine and computer? also, with a set of JBL ceramic headers, and a set of hi flo cats with 3" diameterfrom the cats out with flowmaster, no problems? even with loss of back pressure?