have 2002 Yukon 5.3L automatic 4x4. Whenever I go anywhere, the first half mile is all downhill (I live in the mountains in Colorado). I have to ride the brakes the whole way down even with the trans in low gear because the idle speed is too high. If I go back up, then go down again after it's warmed up, I can put the trans in low gear and idle down just fine. It idles fast when it's cold, then slows down after it's warmed up. Is there a way to adjust the idle speed? Also, is there any way to force the torque converter to lock in? Either one or both would help. I can put it in low range and it idles down nice and slow, but sometimes I don't want to have to use 4WD and it doesn't have a 2WD low range. I also have a 1999 Chevy pickup 5.3L automatic 4x4. When it's cold, it idles slower and holds the truck back better than the Yukon and I don't have to ride the brakes to keep it to the speed I want. The pickup has taller tires and a taller (numerically lower) gear ratio, so it should be worse than the Yukon but it's better. Thanks in advance for any help.

 

Might try Tow/Haul mode. Seems like it holds it in a lower gear. But since you're already in Low, probably won't do anything.

 

My understanding of the Tow haul mode is that allows for slightly higher revs before changing to the next higher gear, but as shark said if you are already in a lower gear not sure how much it will impact.
The Yukon probably weights several hundred pounds more then the truck and that could have influence on the down hill speed also.