I found this and it makes sense t me and my experiance.
"I use to take care a a small fleet of cargo vans for a construction company. We had E350 and chevy 3500. All the guys prefered to drive the chevy, but they required more repairs. If you tow or charge them a lot (like we did) they kept destroying their diffs and eating brakes no matter which discs and pads we tried. Plus the other random repairs. Never had any problem with the transmissions. The 3500 have the 4l80e I beleive, which seems tougher.
The Fords didn't give us any problems (except the random stuff) as long as you kept gas in them. But the guys kept complaining that they felt weaker, less comfortable, harder shifting, more truck like.
I guess it depends how much of a working truck you need. For hardcore stuff, I'd go Ford. If it's for a bit of work once in a while, you'd probably be happier with the Chevy."
Ford Vs Chevy