I mean your adding 3.5" in to the front that's quite a bit

 

This is 3.5" spindle, 2" spacer, 4" blocks and 2.5" lift shackle

 

Sorry I forgot to post back. But yeah, when it comes to lifting a truck inches have a big impact. Idk if you've put the kit on yet or not, but if you haven't you will be surprised how big of a difference it makes. Its going to sit pretty high in the front without any rear blocks. You will see what were talking about when you install the spindles. Unless your rear springs are extremely warn out your probably going to want a 1'' block, but to each there own. You might really like the front sitting really high. I have a picture of the truck somewhere of when I first lifted it, right after the 3.5'' spindles were installed without any blocks. I'll try and find it..

Heres a shot of what It looked liked with 3.5'' spindles and 1.5'' spacers with 3 '' rear blocks and 285s.

 

from a scientfic review. lifting your truck will reduce MPG cause of the more air that will pass under it. You probably wont notice it. Its equvilant to running your AC in the truck. Ive have my fabtech spindle lift since april 1 and love it. And i noticed that these spindles are more beefy than fords stock spindles. so go for it. you wont regret it. i also have the 4.2 believe it or not. it was getting 10mpg. now it gets 13mpg city and 16 highway with bigger tires and lift kit.