We are considering a new tow vehicle.

Everyone's situation is different, for me, my truck is only used sparingly. I pull the boat or camper with it, the occasional trip to the hardware store etc. It's a 2005 and has about 60k miles on it. So for me fuel mileage isn't a huge concern. The thing about an 8.1 versus say a 5.3 or equivalent Ford, Dodge, Toyota etc "small block" is that the fuel economy doesn't drop off as hard while towing. Your 8.1 Burb will likely get as good of fuel mileage as any of the newer SUV's pulling that trailer. However if this truck will be your daily driver then the newer truck will most certainly get better mileage and drive better unloaded. 200k isn't that big a deal if the truck has been taken care of, and it sounds like it has. Your drivetrain is very reliable, it's the electronic gizmos in the GM trucks from that era that you have to watch out for, but not necessarily something that's gonna leave you stranded on the side of the road.