new member with tow issue

[glawton13]

so - I have a 2008 2500 Silverado 4WD - - I use it to tow a small 2 horse trailer. It only has about 40,000 miles on it. This past month I changed out the battery as it died and put in a new one. Now I am having odd downshifting happening while in automatic drive in the tow mode. The worst of this is when the truck downshifts way down when i'm doing about 55 MPH - I'm not braking or changing my pressure on the gas either. When it does that, I put it into manual mode and then upshift it to 5th or 6th. I can't believe this is normal or good for the engine/transmission or the horse riding in the trailer and unsafe in traffic. I have taken it to my dealer who tells me there is nothing wrong and the computer codes indicate no issues. Anyone have any ideas on how to "fix" this issue? I live in Auburn, CA.

[Chris]

Its a "learning" transmission. It needs time