Max speed before moving to S Mode

Don't need ECT for lighter towing, my truck has plenty enough giddy up from stop, and go traffic just leaving it in the S5 mode. All ECT did when i use it ate fuel, while staying in a lower gear way too long. This was on a fairly long ride which i just told myself this is bs, and pushed the ECT button off. I was surprised to find out the rest of the entire ride i didn't require that mode. Truck was much happier to.