I'm a GM fan so I will echo EcoBoosted. As much as I hear about the issue with GM's IFS I've never talked to anyone who had a failure. I put 500k miles on 2 GM IFS systems (granted SUV's not pickups) and didnt have a single issue and I loaded them pretty well. I suspect it's more about the guys that "want" the solid axle (had 2 of those too w/o any issues, but who knows, maybe I just got lucky.
Also i know you said you want gas but i would look at the price/mpg you will get depending on how heavy your build plan is. As expensive as used diesels are the mileage might offset that price differential.
Good luck!