i looked on the rize website and they say it is a front lift and i didnt read anything about the rear. does it come with something to lift the back end or do i need to buy it seperate. and for rims what is the largest backspace i can fit on this lift?

 

yes it comes with blocks to lift the rear but you want an aal to make it sit level

 

17" rims rize recommended the backspacing of 4.5", and any backspacing would work on a 18" or 20" rim

 

I have an fx4 and the rear already sits up higher. am i still going to need an aal? if so what size should i get?

 

That would be a yes, everyones truck sites 2in higher in the back, thats because you have a 2in block, they take that off and replace that with a 6in block, that means you need a 2in aal because your fronts going to drop a full 8ins.