After seeing that many of you have or had a 1500, and after a ton of research, I opted out of buying the 2500 Duramax because I felt that I didn't need it. Then people started coming out on here and saying that they have sold their 1500's and moved up to the Duramax, which I had thought about for a long time.
This is my 5th Chevy truck in the last 40years and in that time I also have had 3 Ford's of various sizes, and still I did a ton of research. As far as high altitude overheating, I had no problem going over the sumits into Flagstaff, Az that top out at 7300', but I did test the trucks fuel to see if anything has changed in the last 50 years... or 49 being that my 1st Chevy was a well used 68 that a friend owned before me. I did notice that running regular fuel over the summits is still a questionable choice. Years ago with my 76 Chevy 1500Crew Cab, I found out that running higher octane really made a difference and that I could get up to 14mpg by using Octane boost on long hauls, over the 8 or so mpg that I would usually get. Now a days, the 76, known as Big Red has been our primary snow plow for the past 30 years and still runs great.
A few days ago, I filled up with regular again, while knowing that we were going to be driving thru the valley and then I put in one last tank full of 87octane to go over the 4500' Oregon/California Siskiyou Summit and it was simply, OK. It made it over but the temp did creep up just a little from normal and my transmission went up from 178° to 196° and the power was simply OK, not great, but still more then enough. Basically the 5.3 litre feels like a standard 350 and tows just fine.
Knowing that we were heading up over 7000', I switched over to premium 92octane, like I've been doing forever and had no problems at all accelerating and keeping it around 65, while going over the Flagstaff summit. The speed limit on that section is 75mph and we had a severe head wind and I have noticed that the gas milage really drops when you get over 65 and you can really feel the force in the cab that's being created at higher speeds with the Ollie in tow, neither of which are that aerodynamically designed to drive at that speed. Most of the time I kept it around 65 going over the summit but I did take it up to 75mph and watched my milage drop from around 7.2mpg, going up at 65 to 4.2 when climbing at 75mph. Still though my 50 mile average stayed around 7.2 mpg over the summit. Then on normal flat ground, I'm getting around 13.2 when towing at 60mph in California, which is a far cry from the 19.4mpg that our Mercedes would average... but that's a different story.
So all in all, I'm real happy with my choice of truck and just like my friend Mark, who has the Duramax, we both slowed way down going over the summit with the 25mph headwind holding us back :)
Running Premium 92 Octane makes a huge difference in the performance of the 1500 Chevy trucks. And if you know beforehand that you will be crossing over a high altitude summit, switching from regular to premium really makes a difference in both power and mpg. So if you own the 1500 and feel like it's dogging over the summits while towing your Ollie,make sure that you switch over to premium for at least that day. Most of the time, when not towing, I just run regular, but they do make Premium Grade Gasoline's for a reason... and that reason is better performance under certain circumstances.
Reed