Best bang for the buck burban upgrade

[homebrew]

Looking for some more ummpff out of my 03 suburban with a 5.3. I had an 02 Avalanche with the same motor which had a k&n CAI, cat back exhaust, and a super chips programmer. With that setup I was able to squeeze out 17.5 MPG, currently the burb is only getting 15 at its best.

Looking to spend around 600, Im thinking of doing a electric fan swap along with a good cat back. Looking for other suggestions(besides buying a honda)

 

[POSJ]

Put a 6.6L Duramax in it...

On a realistic note: Get another programmer on it, computer tuning is the best way to improve vehicles from 01-current. Intake and exhaust might help a little but changing the tune will be the biggest. Are you wanting MPG or power? Those two don't generally go together with gassers.

 

[homebrew]

MPG's are the main goal. I like the tuner because you can gain the MPGs then push a few buttons and get the extra ponies.

 

[POSJ]

I'd do a good tuner, cheap exhaust and intake and call it a day. Anything after that is just a waste IMO. The e-fan could help I guess but I don't know how much $$$ it would cost and be worth it.