The message was a warning that you tranny fluid was getting hot. The problem is that it did not tell you how hot. That is where a Scan Gauge II would come in handy. The Scan gauge can be programed to show the Allison trannny temperature right on the dash. you can watch the temp as you drive. I had the message come on one time as I was pulling a 11 % `GRADE going Into Death Valley, 1st gear, 4200 Rpm's, towing a CRV, but my scan gauge only showed about 220 so I just pulled over for a few minutes and it cooled down right away. I don't think you hurt anything but next time turn OD off and keep the RPM's up and manually down shift to get in a gear that keeps the tranny from hunting. How much does your Equinox weigh?
Scan Gauge II