I have a 91 4wd dakota extend cab v8 5.2l. I am getting around 8 miles to gallon. Is this normal? If you have this vehicle what kind of gas milage do you get?

No it's not normal, however the size of tires and an incorrect speedo could make matters worse without it actually being that bad.

Drive a known mile and watch your odometer, if it's close enough to being a mile, then try this:

Your Catalytic converter could be clogged/clogging.
Your O2 sensor is bad.
Your EGR Valve could be bad, and the hole is clogged.
Your computer needs to be reset (disconnect for 5 minutes)
You haven't checked your computer for codes, or you disconnected the darn maintence light many miles ago because it annoyed you...!
Your tansmission is slipping. (not likely)

Any one of these items can worsen you MPG and quite drastically.. Check your computer codes and fix it! At over $2.00/gal on the west coast, you've got to be hurtin'!

Slantsixness

Thanks for the tips. !!

I think your right I just bought the truck and have not done those things and I dont think the previous owner did.

Very good points.