Odd Transmission Selector Behavior

[coondog20110]

Here's my scenario, I'm towing my 5000 lb trailer in 4th gear manual mode (non-big tow) up to Skyline drive in Virginia. (approx 2000 ft elevation change over a couple of miles) The transmission is downshifting as needed keeping the tach around 2500 rpm.

Near the top and after a sharp 90 degree turn it downshifts into second and the rpms go to 3500 which is the reason I check the gauges.

I notice the square light that is normally around the gear number is not lit. I try selecting a different gear up and down using the manual selector but that does not change the transmission gearing.

The "AT Check" light never came on.

After reaching the top and leveling out, the lighted square returned and I'm able to manually change gears again.

Has anyone else ever experienced this? Do you think it was caused by high transmission temps?

Larry