The chip and tuner folks will promise you more power, better shifting patterns and improved mileage...:S
The only one that is likely to be true is a slightly different {not necessarily better} shift pattern. The energy in a gallon of any fuel is finite. You might maybe get a little more power and you might maybe get slightly better mileage but no way you will get both.
Keep up on the routine maintenance, when you want/need more power put your foot into and drive it as the engineers intended and if you want better mileage slow down, run the proper psi and unload any unnecessary gear.
Greater efficiency is at your fingertips when you simply engage the Tow Haul mode. The weight of any E-450 is sufficient to justify the use of TH even if you are not towing... you are hauling 14,500#. Now put the money you just saved into a fund for any unforeseen repairs that may be coming down the road.
As always... Opinions and YMMV.
:C
