Seems like the something is seizing and thus prevets accelerator from pressing down. I give the pedal a firm, quick stomp and it breaks free. It only occurs while running (with engine off pedal/throttle is smooth)Once free it works fine until next complete pedal return to non-accell (ie. coasting)
Either the pedal assembly return spring or fulcrum, the cable, or the throttle plate is hanging up. All of these can be cleaned up and lubed if necessary. My money is on the cable, but it’s impossible to troubleshoot it from here.
Unintended deceleration!
I couldn’t resist… 
I’ll bet it is crud build-up on the throttle plate in the throttle body. I had a similar problem with my Ford Explorer and my Toyota Supra. The fix is really easy. Just get some throttle body cleaner, disconnect the air hose from the throttle body, and clean the throttle plate and bore with the cleaner. For heavy deposits, a rag can really help clean it out. Open the throttle by hand to really get around the bore and throttle plate edges.
The throttle only sticks when the engine is running?
When the throttle sticks, open the hood and grab the throttle cable jacket. Is it warm or hot? If so, there may be a poor ground between the engine and the body of the vehicle. And if there is, the ground will seek an alternate connection which could be the throttle cable. This causes the cable to heat up which can cause it to bind.
Tester
Have opened thtl body/ appears clean but I will try a cleaner. And this problem is not sticky as much as hung-up mechanically- it takes a good stomp to “snap” it out of locked position. and only happens when running. thtl is completely free with engine off?! Could Thtl position sensor cause this?
Thanks- neither could my wife!!
I have experienced the throttle plate “hang up” also, a good cleaner will help it. However the cable can become frayed and hang up also. But that usually causes the throttle to hang open part way.