mileage question

so i recently installed the following:
3" lift
33 goodyear mtr

after that the truck ran pretty much the same as stock, then two weeks later i installed a K&N intake and magnaflow exhuast and my milage went down dramatically. i live 10 miles from work (all hwy) i filled up yesterday drove home and back to work this morning and im already at 3/4 tank in roughly 25 miles. then i was thinking the computer hasnt adjusted but i dont think it would be that dramatic even if it hasnt. could it maybe be a bad MAF sensor? or do i need to get the truck remaped? i do the R&D for a automotive aftermarket company so im fairly truck savy and do alot of build with trucks with way more stuff than mine on them and never had this issue. but this one has got me stumped, i even hooked the truck to the computer to see if anything was up and nothing was out of the ordinary.

any ideas