Transmission Stumble

[Tim907356]

My vehicle is a 2010 Yukon XL Denali with 129k miles. I think I'm the first one to tow with it, but we bought it used from a street lot, so don't know anything about its history. The hitch looked new when we first hooked up our 5000 lb. travel trailer. It's only been towed 3 times.
I'm on a long trip now, 550mi. away from home (no trailer on this one) but I noticed the transmission sort of stumbles when the engine first applies a load to it. For instance, I can be coasting downhill without pressure on the accelerator, at say 55mph. The tach would read 1300rpm's. When at the bottom, I first begin to apply pressure, the engine will rev to 1450-1500, and then lightly stumble until it fully engages, and the tach drops back to ~1350 or 1400. It happens on every occasion that the accelerator is applied; from stops, around corners, etc.
I just noticed this happening, so it may have been all along, and I haven't paid any attention. We have a long trip ~1400 miles, of pulling the trailer, so I wanted to know whether the transmission is good to the task, or if I should have it looked at immediately.
Thoughts?
Thanks.

 

[drakon543]

to your knowledge has the transmission ever been serviced? does the truck have the aux factory transcooler? should be able to see it through the grill or if you pop the hood and look infront of the radiator. a slight stumble like that i dont think your in any imminent cause for concern. however 5000lbs and if it doesn't have the transcooler could be heating up a bit much. also if you haven't had the transmission serviced i would have suggested to have it serviced a month prior to the trip.

 

[Tim907356]

It has the trans cooler, but the last time we pulled through the mountains of NC, it overheated to 240(max). The engine also overheated when this occurred. I’ve flushed the coolant, and have ordered a tru cool 40000, but it hasn’t arrived yet. I doubt the tranny has been serviced. Is that just a fluid and filter change? I thought I’d do that when the cooler arrived.

 

[swathdiver]

It has the trans cooler, but the last time we pulled through the mountains of NC, it overheated to 240(max). The engine also overheated when this occurred. I’ve flushed the coolant, and have ordered a tru cool 40000, but it hasn’t arrived yet. I doubt the tranny has been serviced. Is that just a fluid and filter change? I thought I’d do that when the cooler arrived.

The fluid should have been changed, especially after the high temp towing episode. The fluid is probably shot and has or will take out the transmission soon enough if not replaced.

If yours were mine, I'd whip out the Tech-2 and check out the transmission readings and maybe even run some diagnostic tests/functions. It may be time for the solenoids in the TECHM to be replaced.

 

[Tim907356]

No tech-2 but I’ll take it in.

 

[GreyStone]

If you enable tow/haul mode on the gear selector does it run any better/different?

 

[Tim907356]

Yes. It shifted earlier and stayed out of 6th. I used it in the hills, but it didn’t change the overheating situations with either the engine or tranny.

 

[swathdiver]

The engine overheats too huh? Well, that's a whole other diagnostic regime and one I would do first.

 

[Costal_Cat]

Yes. It shifted earlier and stayed out of 6th. I used it in the hills, but it didn’t change the overheating situations with either the engine or tranny.

Hey, so a couple of things for you do and or consider depending on your skill level.

I have a 2012 Denali XL and had very similar problems when I got mine towing my trailer. I would do these things some of which you can do yourself.

• Get the shop to do a new Tranny filter. This doesn't change all the fluid but it is a good start and the filter could use it. It is pain not having a drain plug so I let the shop do this.
• Install the TruCool. You need to take off the front bumper cover which is pretty easy. It can be tricky getting the new cooler in place as it is so much bigger. You have to watch the hose doesn't get pinched on the bottom of the cooler with the nipple attached. tricky but doable for most folks
• While it is out it is easy to run the rest of the fluid out bu having someone sit inside turn on and off the engine a few times into a 5-gallon bucket, refill of course
• Flush out the Radiator and replace

If you do all of that and it is not running cooler and shifting better than get a shop involved. Also, I never tow outside of tow mode. For me, with a 28ft trailer or boat, it will always hunt and peck between 5 & 6 and 5 feels like the RPMs are not right. In tow mode, I think it only goes to 4th and the little higher RPMS keeps everything flowing a little better and thus cooler. I live in NC and run a lot to the mountains and down to FL. Before doing the above, and new rear shocks, I was having the same issue. Now it runs a cool 190 at the worst and under on the worst day with the AC on. Without towing on a hot day it really never goes above 150 now.

 

[Tim907356]

I just returned from MD to SC: 550mi., not towing, and the stumbling condition did not change for better or worse. Max temp was 172. I have a tm cooler coming so I’ll prob do the cooler, fluid and filter at the same time. I already flushed and replaced coolant.

I’m thinking about mounting the cooler below the bumper behind the lower grill, in clean air. It would lower the thermal load on all three systems. Any thoughts?