2006 GMC Yukon Transmission Problems - How Hot Should It Run?

Several parts houses have, over the years, sent me warranty claims for crate transmissions that they sold. The majority of the failures were obviously caused by poor installation. Dented pans, chipped tail pieces and broken bell housings were most obvious but kinked cooling lines and plugged coolers and overfilling were common. One truck had the metal cooling lines chopped out and12 feet of 5/16 rubber fuel line was clamped on. The rubber didn’t last long, Neither did the transmission.

I have no idea what’s going on with this transmission as there are always a few unknown details but some points for consideration might be.

Overheating fluid due to slipping. The fact it was rebuilt with a ton of new parts by a well-establshed shop does not necessarily mean the job was done correctly.

Dragging brakes?

Possibility of the converter being the wrong one or not seated properly? Normally I wouldn’t put too much into a statement like this but I’m reminded of the Subaru that came to me some years back. In this case a shop had pulled the engine to change the head gaskets and the converter had become dislodged on one set of splines. (This model had 3 sets) The shop apparently though the converter was on all of the way.
The car owner drove around for several months until one day it made a loud whirring and scraping noise and then quit moving. It was towed and when I removed the transmission I discovered the entire center of the flexplate with all of the mounting holes had been torn out.
The car owners said that the car had been fine right up to the last seconds before it died. (This scenario is grasping a bit, just pointing it out.)

Just my opinion but the transmission shop changing their story numerous times does not reflect well on them and one thing did strike me as curious. You state the transmission shop has been around for 30 years but a look at the BBB site shows they have an A-minus rating due to the length of time they’ve been in business and the business start date is listed as March, 2009. ???

I was very proud that we kept comebacks down to <2% year after year. But those who owned the comebacks were disappointed. My secret was to jump on them and straighten the problem out immediately regardless of the cost and thank the customer for their patience. That approach was very beneficial in the long run. But many shops are more attentive to the bottom line on a day to day basis. That seems a shame. I cannot judge the integrity of the shop you are dealing with but since their integrity has been questioned here I must admit that I too see reason to question it.

I know the guy that owns the business has been doing transmissions for 30 years, but I guess this particular business has not been operating for nearly that long. I got the vehicle back today with the new gauge installed so I will need to see what that tells me. The problem is that I have never had the transmission warning light come on unless I am fully loaded and towing my trailer and the next time that it going to happen is May, so I am really in a “wait and see” mode from now until then. I have made sure to let the shop know that if the the temp goes over 200 (per the comments here) I am going to expect him to do something about it, whether that means installing a larger cooler or something else. Thanks to everyone for all of their input on this issue. You guys have been incredibly helpful to a guy that used to know absolutely nothing about transmissions and now feels like he has at least a baseline knowledge of what is going on. THANKS!

Another possibility (sometimes referred to as a WAG) could be that the fluid is not circulating out of the transmission and through the cooler. By this I don’t mean that it’s not circulating at all but rather that it’s not flowing as much as it should due to a pressure problem and which could also cause slippage. (Incorrect valve body gasket, warped valve body, obstruction that the cleaning process missed, etc.)

The above is just more theory at this point and you might keep us informed as to how this pans out because for 3 grand plus you should have zero problems in my opinion. Best of luck.