We have two Expeditions that we tow a 4200# dry weight trailer in the Rockies and have no problems doing it. There is no 3/4 ton class of Expys but there are Expys that have that kind of payload. Our 03 has a 1565# payload and the 07 has a 1746# payload. The highest I've seen is over 1800#.
The 03 will slow down on the steepest hills but it has the less powerful motor and 3 speed tranny. The 07 does better with the better motor and 5 speed tranny. On the flat either has more than enough power and I have to watch Keeping the speed of the rig down as I tend to keep up with traffic.
I've never towed with a Burb but my family does and they like them as much as we like the Expys. Renting a Burb the last time we were home, it seems like a nice truck.