I had to go on a 423 mile trip and I plugged in the scanner for a bit and took some readings. The STFT didn't go over 3.9 on one reading, 1.6 on another and .8 on another, I had cruise control on. As soon as I canceled cruise control with my foot not on the gas pedal, it would spike to 25. While cruising, the STFT stayed on those low numbers with no spikes at all. I was going 70+ mph for those scans. It seems the spikes came when the load dropped or no load. Since cruise control was on there was always a load and no spike.

My scanner is small, each reading is a little over a mile, but the STFT stayed low for a while.

By 'load' do you mean the car making an exertion to increase speed or maintain speed against a tendency to lose velocity? So when you cancelled cruise control and didn't step on the accelerator (meaning you let the car gradually slow down by itself), your STFT spiked? I thought one had STFT (beyond what one naturally have when idling) only when one stepped on the accelerator.

O sorry. I have just re-read your post more carefully. You actually mean when you cancelled cruise control and control your own speed by using the accelerator your STFT spiked to 25% (but did it happen fairly continually, though, or if it happened only at that moment when you first went off cruise control and stepped on pedal?).

I went cruise, then I hit cancel button, never touched gas pedal and then resume or set on this one. Didn't slow down much.