So, I've done a couple 4bt gmt400 swaps. My personal truck was a '92 k1500 reg cab. The truck dyno'd 496hp at the wheels. I towed above max truck capacity with it, and the good old 10 bolt rear axle held like a champ. I did flex the frame enough that the windshield cracked. So that's an issue on the 1500 trucks!
Another one I did was a '95 k2500 ext cab. Nv4500 double overdrive, set at 275 flywheel hp, it towed a 30ft lawn mowing trailer with ease, and empty truck got 29mpg when I took it on a trip.
All in all, I'd tow with a 4bt, just understand it is a 4cyl, it needs a little more rpm than the 6bt to make it's power. Slightly vibrational, but injection pump tweaks and fluid dampers work wonders on these things.
For a 1 ton truck, I would NEVER use a 4bt. Continuous wringing at max effort does cause shorter engine life.
Hope this helps give you a little insight on what a 4bt "can" do.
