I just traded my 1997 GMC Savana Conversion van for a 2008 Ford E150 Regency Conversion van. What a difference a decade makes! That 5.3L V8 gets 21 MPG on the highway! My GM didn't get 21 MPG rolling downhill in neutral.. with the engine turned off.
And GM, at least in vans, makes the worst A/C ever to try and cool a vehicle. My '97 Winnebago is built on a GM chassis with a 454 and I think my Ford Ranger 4-cylinder has more power.