> It would always come on after I got off the interstate and coasted up the on-ramp, so I am not sure if it came on after getting hot enough on the interstate or if it was just the coasting that caused it.

I suspect you may have had a very regular time/distance in the repetitive sequence of [reset code, drive some amount, code comes back]. For low-priority codes (unlike major engine emergencies) the ECU will use a "fault frequency" counter to suppress nuisance check engine lights that don't actually need fixing (like if a sensor was briefly out of range just once, a fluke rather than indicating a problem). So if it increments the fault frequency counter for that particular problem once every 10 miles of the fault actually happening continuously, and doesn't throw a check engine light until it counts to 6, then the light will come on after 60 miles. Just making up numbers but you get the idea... so if you always reset it that much driving before the same on-ramp, then it will always light up at that point. Also, the fault frequency counter might reset with every drive cycle, rather than just at the point that you cleared the code. Taking a detour during the same drive cycle as the on-ramp (as opposed to relying on variance of how long ago you did a reset) would be a good experiment.

But if you know that the drive cycles weren't so regular, then it could indeed be related to overrun fuel cut (coasting) or whatever.