Well after towing my 11,400lb 5th wheel and getting 12.7 mpg, no way will I tow anything with a gasser again. The difference is remarkable. Had my BIL behind me towing his 9500lb 5th wheel with his '12 6.0 gasser sitting between 4000-4500 in the hills, and I am sitting comfortably in the 1800-2000rpm range, with tons of power on tap.
Talk about no longer being stressed while towing.....
For pulling a travel trailer behind a Surburban, I seriously doubt there is a better combo than the Duramax and Allision, 5 or 6spd.
For the OP, that is one clean looking swap. Congrats on a job well done. Mind posting what the total cost was? By the way, as I was re-reading over this thread, it's a good thing you didn't get an 05 or similar Excursion. It would have had the 6.0 Powerstroke and could have given you a nightmare of repairs.
What kind of mileage are you getting, and how did that compare to the 6.0?
Funny thing is I have a neighbor that has what has to be rare, a Blazer, that came with the 6.5 GM diesel in it. I guess it gave out, and he swapped it for a gas engine. I don't get that personally, since he has a Ford and Dodge, 1 ton diesel trucks. Why go gas? Less mileage, less power, and if the state ever found out it would have to get smogged, it currently does not. The title still says diesel, "exempt".
It looks like a prime candidate for a Duramax/Allison swap. Old enough to be exempt from smog. A Duramax with no smog equipment, no CAT, no EGR all legal, well sort of. Hey, I bet maybe 1 out of 500 DMV employees would look at a Dmax and know it wasn't the factory motor.
Of course, you'd probably have to upgrade both axles, since the 6.5 didn't put out near the power.