2008 Yukon Denali XL tow issues/ vibrations

[MrMushu]

I posted part of this in general discussion but wanted to go further into details.

First off the new to me denali has 130k and seemed to be in decent shape. My first issue is while in tow mode pulling my nearly 4k pound boat the transmission wants to stay in the lowest gear possible. It lets the engine rev past 5k with very little throttle. I let off the throttle and it will to to the next gear but if I give it any throttle it gears down again.

Second, it will not go into manual mode at all.

Lastly... I'm getting vibrations from what seems to be the right front when turning right and really cutting hard left. Also getting some vibrations at highway speeds that I'm thinking are the crap tires. The right front also makes a clunk noise when going over bumps.

 

[swathdiver]

Tow/Haul is only of benefit when you're at 75% or more of rated capacity, which in your case would be at or above 5,900 pounds. It does hold the gears longer.

Don't know why it won't go into manual mode. Vibrations when turning could be hubs, axles, tie rods, sway bar end links, etc. You're going to have to get her up in the air and check all that out.

Tires dry rot and whether they are bad or not need to be balanced as they wear.

It's possible that there is an issue with the transmission, internal codes stored, and that is preventing manual mode and affecting Tow/Haul. See if you can get someone with a good scan tool to check for any internal transmission codes for you.