Alright what weight of oil are you running? that will make a difference in the vortecs as well. You also didnt tell us what you did for tune up stuff, such as plugs wires? things of that nature.
As to a programmer well the big question there is and in reality is how many miles per gallon you will get versus the cost of the programmer. If you are buying one for multiple reasons then you will be good but just buying one for milage it will never really pay for itself.
Also i thought the 03 up had elec fans? i thought they did that when they changed to the drive by wire in 03. interesting.
The 04 Regency I had didnt have electric fans. My buddys 05 z71 doesnt have electric fans. My 06 had them. Weird thing about drive by wire, it isnt on 4.3 trucks all the way up to 07.