Umm I daily drove both my Van and my Tahoe. 30-40 mile commutes each way every day. I drove the van or Tahoe 3 or 4 days a week and my Titan and my M56S 2-3 days a week. I had the Tahoe up and running and the van was down at the time. I had the 2012 Titan and the Van at the same time and drove them back to back. I drove the Tahoe and the M56S back to back the same way while I rebuilt the van as a 1-ton with the 383. Tahoe is about to get the 8.1L dumped back into it. Years ago I also swapped back and forth between my 1983 G20 van and my 2006 Ram when I had the Ram. In the heat of summer, I usually drove the G20 van every day. Sit in bumper to bumper traffic on a 108F day where the air above the road is 120-130°F. That will test the best ac systems. The absolute worst AC was my 2006 Ram closely followed by my M56S when it had the stock engine tuning. Nissan/Infiniti chose not to command more than 60% duty cycle on the electric fans under 20 mph, which resulted in poor cooling when the vehicle was stopped. The absolute BEST AC I have ever had was in a truck that the vents did not blow well in. However the system would freeze you out because the air would blow so cold and the truck was white. It was a regular cab 1994 Dodge 2500 V10 and the condenser on that unit rivaled the size of one on an 18-wheeler, massive and it had a large engine driven fan. I have been on 1,000 mile or more long trips in every vehicle I have ever owned. The most comfortable vehicle to drive on long trips was my 1983 G20 van hands down. AC would freeze you out, it got good mileage for what it was, the engine was quiet with 3.08 gears and the 700r4 and later 4L60E, and with the old over assisted GM power steering system you could guide it down the road with a single finger while it floated down the road. With 200K on the stock 305 and 700r4, I never worried about it. Even took it on a 3,000 mile road trip towing a small pop up camper trailer. I kept a few quarts of oil and a simple tool box with me. On one trip I had to change valve cover gaskets at a KOA I spent the night at. On a different trip I had to replace a smog pump that seized up and took out the alternator belt. When I realized the alternator was not charging, I shut off everything and I made it 100 miles without a belt on the alternator to the nearest town. Saving grace there was it was day light and the only thing the battery was running was the HEI.I see many 'experts' on this forum that really crack me up. Most don't even really use their gmt400. Bolting them together and taking pictures of every little ******* step isn't actually the same as using it on the road.
Example - you'd have to drive a gmt400 in the same exact setting as the f550 and then compare...
I do that often with my f150, a new duramax, and have used a newer 6.2 F250 too. The results are - the airflow in the old gmt400's isn't very good. You can really improve things by insulating etc, but then the windows start to fog, cause the airflow just wasn't designed to work very well. It still works ok. You won't sweat to death.
All vehicles have good and bad points - just the way it is. I love my gmt400. Not enough to stick my head in the sand though.