I just got rid of my 2001 3/4 ton Yukon XL it had the 8.1. I got a great deal on it when I bought it because fuel had just hit $4/gal (2009ish). People called me crazy. I needed a large SUV and the motor was a plus. Didn't pull much, but when I did, I needed the big motor. Didn't care about mileage. I averaged 11.5-12 unloaded and 6.5-9 when towing (10K camper, 5K Aluma sled trailer, 6K car hauler)
I replaced it with a 2008 3/4 ton Suburban with the 6.0. Not impressed at all with the 6.0. I had plans for it when I bought it (knowing the 6.0 was under powered). I sent the suburban to Duraburb for a Duramax conversion. Suburban was a 30K mi truck. I found a 2008 donor with 49K mi and had the entire driveline swapped in.
It is my first Diesel and I love it. There have been a few quirks as one might expect with a swap like this, but nothing major. It has an EFI live DSP-5 tune, 4" exhaust and full delete. It is fast and pulls like crazy. I average right around 19-20 unloaded and 10.5-14 when towing (hand calculated). It is awesome when pulling through mtn passes and it up shifts when going up a 7% grade and just keeps pulling. My 8.1 would make it, but I always felt like I singing "I think I can, I think I can...."
I knew they were more expensive to fix, so I got a low mileage donor. To me it is worth it. I've enjoyed everything about it so far. The new diesels are much more reliable and with less problems.
Mark