You don't want a V8, but you want a Lightning..........I'm confused.
You want fuel economy but are asking about chips
Pulley changes and programmer gets you 450 SAFE HP.
They're rated at 5,000 towing. 12-15 MPG is more realistic (that's on our box stock '04)
Good luck finding one that's not a rat for 13K...............19K will get you a nice early Gen II L.