Based on what I'm reading here:
1) You have replaced your pedal with a new one
2) you do NOT have a pedal commander or other throttle control accessory
3) The dealer is unable to replicate the problem, and has not been able to provide a reason why (no surprise)
4) This started happening after you vacuumed the truck once a while ago, and has been intermittent since.
All of this usually indicates either a lose pin or wires broken inside the pin (so that the wire winds up only having a few strands actually connected inside the pin - all the others are connected intermittently at the break, but when too many are not, it causes the voltage passed by the wire to be lower than it should - i.e.: out of tolerance) to the pedal or the TBC, a lose or dirty connector (causing lower voltage on that channel), a bent or lose pin, or a wire that is shorting out to ground in the harness (it happens - usually when a wire rubs regularly against something sharp).
The Pedal gets +5VDC in on two channels, and sends out put through two resistor channels: as you press the pedal, less resistance means more voltage is sent to the PCM.
Both channels should be the same (within a few mV) voltage of each other.
If one channel is out of tolerance from the other, it triggers the DTC, and puts you into limp mode - mainly to protect you from a faulty pedal causing unintended acceleration - which could of course cause you to wreck.
If the internals of the pedal are bad, or one of the resistance channels is failed or failing, the voltage across that channel will be much lower than the channel that is working - again, this causes an "out of tolerance" situation, and you get put into limp mode - throwing one of the 21xx codes usually.
Since the pedal is the only part that moves in this circuit (your code will throw before the throttle side of this is involved because the PCM will detect the error before it sends output to the throttle) this is the most likely failure locations.
Since you've replaced the pedal, the next part would be any connectors that are in the circuit - the closer a connector is to a moving part, the more likely it is that it could have premature failure - leading to the wires where they connect to the pins, the pins themselves (bent, broken internally, or lose - the pin MIGHT look fine, but it could be bad - and you'd not know it), or the connectors not seating correctly.
Check for +5 VDC at each of the supply side pins, and verify you have good ground on both ground pins. The signal pins will be more difficult to determine if there's a problem, but I believe you can use AlphaOBD to monitor the output through the PCM.
I've attached the wiring diagram for the circuit in case you need it. The pedal side is exactly the same across all models with possible exception of the pin numbers on the PCM/Firewall.