The limp mode is engaged when the ecu thinks there may be a condition where driving the truck is dangerous or to protect damage to the engine. In this case, maybe it detected a fault in the throttle input and limits the throttle signal to a very small % to prevent uncontrolled acceleration. As far as I know, the only way to get it out of this mode is to clear the fault. In your case, maybe just a short drive plus a restart was enough. You might try pulling the negative terminal on battery for a few mins and see if that causes the truck to do a full retest of the sensors.
Good luck man, bring a laptop with Forescan with you in case you need to pull the code. Video is also a good idea if you see this again, so you can show the dealer.
