Replace a Vortec 6L with an 8.1L

Hello all,

New here, I've searched the forms but couldn't find any answers so maybe I'm just crazy for asking this but here goes ...

I have a 2007 Chevy 2500HD Classic - Crew Cab, Long Bed gas with a 6.0L engine, only mods are a K&N CAI and Diablo Predator tune (towing). I use it to tow a 2008 Jayco 32BHDS weighing in at about 8700lbs loaded. I plan on keeping both around for a while and would like to get some better gains when towing without replacing the truck (towing capacity is 9700lbs). Not sure what else I could do but upgrade to a 8.1L engine which is a standard upgrade for this truck (from what I read). This would give me a towing capacity of 14,800 which puts me under the 80% mark. I typically tow in 3rd since it will just downshift on any little incline. I was hoping the bigger engine would give me better take off and help hold the truck at lower rpm's when highway towing (i.e. preventing downshift). I get about 7.8mpg when towing and 11.2 on a daily basis (only 5 miles from work) so increase in mpg would be nice but I know the 8.1 would be null if not less?

So after my long winded story my question is - has anyone ever replaced their 6.0 with a 8.1? I know a duramax 6.6 isn't possible due to the additional weight/suspension needed to support it, right?

What other options do I have?

Thanks!!!

---------- Post added at 09:35 PM ---------- Previous post was at 09:29 PM ----------

Oh, and I forgot to mention my truck has 43K on it so I would hope I'd get a decent price for the swap