Suburban Versus Excursion or something else???

For the last several years we've been towing our 2005 Outback 26 footer with a a 2WD 04 Suburban with the 5.3 engine. Towing, we'd get about 10 MPG and although the rig was fine on the flats, it would dog on the hills, like the Grapevine in southern CA and slow to about 40 (loaded with all our gear and the four teenage kids plus wife). When the 'Burban rolled over to about 220,000 miles I wasn't keen on taking another six week cross country jaunt in it, and it's been pretty beat up now teaching all the kids to drive. So we started looking within our budget for a new tow vehicle to at least get us through last summer's trip. We ended on a well kept one owner 2001 Excursion with 179,000 on the odometer and a V-10 engine. I figured this rig would suck up the gas but run circles around the towing power of the 5.3. Boy was I wrong! Not only did the rig drop my mileage to about 7 overall when towing (which was fine - I expected it), I also found it to be just about as gutless as the Suburban was on the grades. So, our search has sort of continued. We're not into the Excursion for a lot of money - about $8000 - and we are in a position this year to go upwards of $15-20,000 if we find the right tow vehicle.

My wife doesn't want to go with a truck - she wants the capacity to comfortably carry the whole family for the long trips six now adult-sized people for 4-6 week trips), and I want to make sure that the vehicle we get will handle up to at minimum an 8000 lb trailer plus the family. She would prefer that we keep options open and gt the best tow capacity we can on an SUV as she would like to upgrade the trailer to one where we don't have to pull our queen bed out every night or climb over one another to get into the bed. She REALLY liked the roominess of the Excursion and so did the family.

So the question then is, what are our options? I'm fine with an older, well kept, vehicle, but would like to at least be able to hold my own on a moderate grade like the Grapevine at 55, or the ones you hit on I-80 coming across Nevada and back into California. I'm open to a diesel, but have heard too many horror stories about the 6.0, so I want to stay away from those. We've considered an Excursion with a 7.3 diesel, a Denali/Yukon XL with its larger 6.0 gas engine as well. Anyone out there got some experience with those vehicles and the background to compare with my experience towing with the Excursion V-10 and the 5.3 Suburban? I was thinking the 6.0 gasser just to get a little more power out of it on those hills. Our trailer itself is probably 6000 lbs. Yes, I'm a bad RVer - I've never weighed it, just based on the dry weight (4500 on the sticker) plus what we haul around with us. It's always towed just fine with no sway or other issues. In either the Excursion or the Suburban, on the flats you don't even know it's there unless it's super windy.