I looked at a Jet chip for my Ramcharger, and was told it was basically junk - the ECU is "the thing," and I ended up getting the MOPAR Performance ECU for it, so I can run a hotter cam eventually.

For MPG, I'd stay with a Superchips Flashpak. Over here in Pittsburgh - where I hit stop signs every 5' here in the South Hills - I find driving with the tow/haul underdrive engaged, works best if I'm driving > 45mph. Helps the Commander get out of its own way!