When I bought my van, all I towed was my Jeep and I thought my 5.4 was just fine power wise. Recently though we bought a toy hauler to transport the Jeep in. Now I find that I don't necessarily need the van built out the way I have it, and I'm dreaming of more power.
We'll see if we use the van on road trips, and the trailer for those Jeep trips. If we do, I'll put up with the lack of power when pulling the trailer. But if all our trips evolve to towing the trailer, we may put the van up for sale and build a new van. Hell, we may do that anyway...
My buddy that has a 2003 7.3L 4x4, high top, custom interior similar to mine, has just purchased a Chevy Express 6.0L. His only plans are a 3" Weldtec lift, remove a couple seats inside, and add a chest style fridge.
Driving his Chevy I'm impressed with the power and handling. I would bet that shorter rear wheel to back bumper would tow a trailer better. The doors sound tinny compared to our Fords. Some Dynamat should fix that though. The interior in general feels cheaper than the Fords. Still, I find myself building a Chevy in my head. That 6.0L is a sweet motor. This new motor I'm sure would be even better, but I'd have to wait a few years until it trickles into the used market.