, I usually use cruise control and on the 4lane run at 65mph. Sometimes with Tow/Haul on, the trans doesn't want to go into converter lockup. I find it hard to get better mileage (above 20 mpg) while towing, if the engine RPM is much above 1500.
I agree with you that it seems like better mileage can be had with the cruise off but I find it less restful. I just play with settings until the converter will stay in lockup then go to cruise control.
The Chevy Colorado was born to tow. You may appreciate all the engineering that went into it for towing. Yesterday I finally found that the alternator is rated at 140 Amps. With two 75 amp/hour AGM batteries, The batteries are always at full charge even with the fridge on DC. As you may already know, in Tow/Haul mode the alternator is allowed to put out 14.4 VDC to keep the trailer batteries charged. The trailer charge wiring is 10 gage and fused at 30 amps. They even provide a dash display for voltage if selected.