I'm currently running a MPG tune on my 2017 Ford Fusion Sport.
Tuner is a BDX Rev X from Unleashed Tuning.
Unfortunately I'm starting with a twin turbo 2.7 V6 so not a ton of improvement to be had. From what I can tell most of the gains are from the transmission shifting, stock under light acceleration my car would rev up to around 2700-3000 rpm before it shifted, (even when accelerating down hill), now closer to 2000, but it raises with pedal input.
Improvements are around 2-3 MPG's, more in the city and slightly less on the highway. I'm averaging 26ish, most Fusion Sport guys are low 20's
I just reloaded the MPG tune last week, during the summer I run a 93 octane performance tune for fun.
If you research I'm sure there's a tuner for your vehicles, you'll have to see what's available for your older ones.
Probably not much for your van, the newer the vehicle most likely the easier it is to tune.
Crown Vic Tuner
https://5startuning.com/product-cate...r-programmers/