I had an '01 Suburban 2500 8.1L with 4.10 gearing pulling my 7000lb loaded TT. It was amazing. Got right around 8MPG towing.
Recently had to give up a '14 Ram 3500 CTD and GD Reflection 5th wheel. It also towed amazingly well. LOVED the exhaust brake. Around 10.5MPG towing 10,000lbs.
When towing out West there are mountains everywhere. The Ram devoured climbs. The 'Burb was no slouch....found it's sweet spot at 3100RPM and cruised to the top.
On the flats, which let's face it is probably between 90-95% of travelling, both combo's chugged along effortlessly.
Those are my experiences, yours may vary. :)
Now, once we make it through to the other side of our 'life detour' I will be hoping to get back into towing.
Because funds are an issue I would have NO qualms about grabbing another 8.1L if it presented itself.
A 2500HD would be awesome, and there's even a Yukon XL in my area in the low $5KCAN range which keeps bouncing into my conscience...lol
Now, a 'modern' F150 3.5EB (which has been mentioned in this thread) seems to fall in the $20-30KCAN range here depending on year.
For me, it'd be a no-brainer. Grab an 8.1L, run it on synthetic oil (which seemed to illeviate the oil consumption on my 'Burb) and cruise on. :)
If money wasn't an issue, then my plan might be different, but it is, so that's that.
My thoughts,
Mike.....off to search CL for 8.1's......dang-it :D