2004 Suburban 1500 towing issues: Engine or gears?

[Fless]

Local guy here, experiencing the same with my '04 5.3 Flex Fuel, 3.73 gearing. When I towed (always in Tow Mode) my popup -- 3100 lbs gross but never loaded to that -- the high mountain passes weren't too much of a problem, although I've not really been happy with the throttle response and shift points even when not towing. They're too far apart and it seems like one has to mash the pedal to get a downshift before low RPMs become an issue. Then, of course, the high RPMs and screaming begins. I don't think 4K RPM is a problem, and I think that's a good spot in the power band if what I'm reading is correct.

I sold the Pup, though, and recently towed a TT (Viking FQ17, IIRC) that has a gross weight similar to yours. The extra weight amplified the issues with power loss at high altitudes.

I plan to get a tune to improve things, especially throttle response and shift points. Part of the factory tune on these is to maximize fuel mileage so better response suffers from that.

For the time being I've learned to slow down a bit and not expect to keep up with the cars.

 

[SnowDrifter]

Don't judge me for my taste in cheerios

Nah but on the real... I wonder what's different about the air composition at altitude then, if simply pressurizing it to sea level doesn't yield the expected power improvement

 

[Scottydoggs]

its less air over all. at elevation a engine is like you trying to breath through a straw while running as fast as you can.

why people get out of breath so easy when they travel up so high too.

also why fighters train at elevation, they get used to working out there when they come back down they can now take more oxygen to their muscles giving them a larger gas tank so to say. or insane cardio.

 

[Fless]

Air contains 20.9% oxygen at all altitudes; lower air pressure at high altitude makes it feel like there is a lower percentage of oxygen. As @Scottydoggs said, less (thinner) air overall so less oxygen.

Here’s a chart of “effective” oxygen % at various altitudes:
https://www.higherpeak.com/altitudechart.html

At 10,000 ft. in elevation one would experience around 30% less effective oxygen (than at sea level) in the reduced air pressure. Gotta have the oxygen to burn the fuel. It's why high altitude athletes acclimatize whenever possible.

 

[Josh61513]

4.10 Gears would help keep you in 2nd, but would decrease your speed in 2nd gear proportionally (about 10%) for a given engine RPM. And especially being 4x4 (2 axles) that’s probably cost prohibitive especially being a higher mileage truck.

Unfortunately there’s not a lot of low hanging fruit here without spending more than it’s worth.

Decrease your drag if you can-run your truck and trailer tires at their max pressure. Make sure your engine and trans are running as good as they can-clean air filter, synthetic engine oil and fresh Dexron in the transmission.

Keep your weight in the truck and trailer to a minimum.

A tuner may help a little but I doubt it will be enough to keep you in 2nd gear.

Other than that unfortunately I think your most logical move is to run the truck as-is until you can trade for a same year Suburban with 4.10 gears, upgrade to a 6L powered Denali, upgrade to a newer 07+ Suburban (with 4.10 final gears of course!) where the 5.3L got more power, or upgrade to a 2010+ with the 6 speed transmission and max tow package. Amy of those would give you noticeably better towing performance. Dumping a bunch of money into your current rig may leave you disappointed with a lighter wallet.

https://www.trailerlife.com/wp-content/uploads/2012/01/Trailer-Life-Towing-Guide-2004.pdf