I don't know if this would apply to a truck, but I once had this problem caused by a broken seat mount in a 52 Chevy sedan.
When the car accelerated in low gear, the seat would rock back slightly. This would lift my foot off the throttle. The car would then decelerate, causing the seat to rock back forward. This would drop my foot back onto the pedal, and the cycle would repeat.
Kinda fun when your 15.
I suggest you take a moment to rule out this possible cause before spending any serious time or money.
regards,
Leon
