Some of that reminds me of early days with my Suburban . The reason in my case was a higher than necessary level of fuelling in OFCO. Mine runs on LPG (propane) and the OFCO isn't necessarily set at zero. A setting higher than zero aids transition going back into the throttle. Too much and it feels like it's trying to run away.Just took an hour drive on some 2-lane. Speed limit varied from 35-55. The truck almost acted like the cruise was set. If I was going 45 or faster I could take my foot off the accelerator and give only minimum input with the pedal to keep it at 45 or so. I had the ac on and i could feel the truck increase/decrease in speed as the compressor clutch kicked on and off. It took either a significant hill or brake pedal to slow the truck. Going downhill, it was a runaway; it would gain rpm and engine speed as long as I let it. Had to use a lot of brake to reign it in. The brakes will stop the truck, I don't want to sound like I'm being totally reckless.
truck.
Are you sure yours isn't somehow pulling fuel in on a closed throttle?