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Transmission making noise

I have a 05 GMC sierra 1500 4DR 2x4 i was pulling my 91 GMC with it, after the towing was complete the truck sat for 2hrs±. when i drove it again I got to 65mph, then slowed to 40mph. it started grinding I pulled to the side and it was whining, this happened with in 10min of driving. fluid is to top level but the noise is there, and its there when parked but louder when in drive, and at a complete stop. when at speeds avobe 50 it goes away any ideas?

Please confirm which truck is giving problems? The tower or the towee?

The 05 GMC sierra the tower sorry

How does the fluid look? Maybe very dark… When towing was the GMC in Overdrive? And was it possibly “hunting” continuously between 3d and OD? I will be watching closely for the Transman’s opinion but my first guess is the lock up clutch is trashed.

If the noise is there with the tranny in “park”, vehicle not moving, then it sounds more like the torque converter or it’s lock-up clutch has failed…

Fluid is clear redish color i was going 50 tops i did have couple red lights and i did forget to press the towhaul button. That clutch is it expensive fix?

In any event, the tranny will have to be pulled…If it’s the torque converter, that’s not TOO bad…If it’s the overdrive in the tranny, you are in the $2500 neighborhood…

Thank you for the replies i will take to competent professional

Check to make sure 4wd can disengage, I doubt you were in 4 low but maybe making sure you can get into 2wd again will help.