Question about dbw throttle hanging

[Moofus02]

It's not a chevy it's a t880 kenworth with a cummins. I've been noticing that when I back off the go pedal there is a delay before it cuts the fuel. I'm curious if it's the pedal or programming. I've had one run away a few times for 5 seconds or so at full power. Just did it to me again in a tight parking lot yesterday. Not always the same truck. They always blame the driver. Years ago I had a pedal in a cat die and the default is wide open on them. I think I've got a pedal transducer or whatever there called getting bad?