poor gas mileage and check engine light on my '95?

I have a '95 2.7 L 4WD with a manual trans and 144 K miles on 'er. It has a 3" body lift and 32" mudders.
The check engine light is always on and the mileage is REALLY POOR, well below the published values. I know the oversized tires probably account for some fuel inefficiency but still...I heard from some mechanics that its the MAF sensor needing to be replaced...I tried this a couple years ago (with an expensive unit bought from Advance Autoparts) but it didn't work! Can somebody tell me what's the deal? She runs great otherwise, hoping to solve this problem w/o dealer/mechanic expense...

Thanks!
-Olly

 

exactly, without the codes you are shooting in the dark. the codes will point you in the right direction.