I wonder if its the receiver and servo blipping - may have a short somewhere or damaged antenna wire (you didn't cut the antenna wire, right?)

or the engine bogging at full throttle.. - engine needs to be tuned

also, go through the truck and check for loose screws or aluminum parts rubbing - could be radio interference

do you have another radio/receiver you can test with?
does it do the same if you full throttle it with the truck lifted off the ground?