asilverblazer

That's a lot of brake dust for OEM pads... I can't really make out what motion is making the clanking sound in the video, either way that isn't normal either.

DTC P0650 or DTC P263A The ECM detects low voltage during the MIL control circuit driver OFF state. This indicates either a shorted to ground or an open MIL control circuit. gmupfitter has wiring diagrams to reference. Looks like you need to start looking for damaged wiring in the MIL circuit. It seems that the MIL circuit is damaged/pinched with the camera circuit.

Nice, the thing that annoys me on the previous style trucks is how you have to cut a radius on the end for the boards to lay all the way down to the bed floor.

I think I understand what you are saying. In 4H with the transmission selector in L1 it will allow the engine to control vehicle speed better than in D, where it would upshift automatically. Going downhill it could exhibit some additional control, and could limit wheel spin speed when accelerating on slippery surfaces. The bold portion above... I generally disagree with because of the (IMO) significant difference in gearing; I understand your comparison and suggestion of similar mechanical operation.

Not as effectively (if not at all) - the low range in the transfer case significantly increases the mechanical advantage of the engine.

Based on code P0451, that is how I would proceed.

gmupfitter has wiring diagrams to view... However, I would focus on the connections and look for other obvious wire/harness damage first. A random broken wire is much less common to require a replacement of it. The code (P0451) is very specific to not being able to determine a correct 'zero' value and suggests that other elements may be preventing that (crimped or obstructed hose). Since your scan tool isn't able to properly test for those faults, the above post would be the next step (we are assuming there is no fault vs. testing and confirming there is none) and checking the electrical circuit. Because proper tests haven't confirmed all else to be OK, I wouldn't spend a significant effort to chase down a potential electrical circuit failure that isn't very likely. Unplug it and look at it... see what you think. maybe clean the pins connection. Perhaps just some basic checks, disconnect the sensor and verify the appropriate voltage/resistance per the post above at the connector pins. If a deficiency is found, probe the backside of the connector/wire. The likeliest electrical failure points I think would be the connection to the sensor or the sensor itself. Narrowing down the 'likeliest faults': 1. Obstruction or other condition preventing the sensor from getting an accurate reading. 2. Sensor electrical connection. 3. Sensor failure. Based on that, I would buy a new sensor, crawl under the truck with the intention of replacing it and doing so unless I found an obvious problem with item 1 and/or 2. If the problem remains, then I would start chasing that circuit in more depth. Keeping in mind that testing for obstructions in the EVAP canister or vent lines hasn't been fully completed.

I've bought new batteries that are bad.

Looks like all that boiled down is check the wiring then either ECM (not likely) or the sensor... in addition to:

Circuit/System Verification Remove the fuel cap. Ignition ON, engine OFF. Verify the scan tool Fuel Tank Pressure Sensor parameter is between 1.3 and 1.7 V. If not between 1.3–1.7 V Refer to Circuit/System Testing If between 1.3–1.7 V Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data. Verify the DTC does not set. If the DTC sets Refer to Circuit/System Testing. If the DTC does not set All OK. Circuit/System Testing Ignition OFF, all vehicle systems OFF, this may take up to 2 min, for all vehicle systems to power down. Disconnect the harness connector at the B150 Fuel Tank Pressure Sensor. Test for less than 5 Ω of resistance between the low reference circuit terminal 2 and ground. If 5 Ω or greater Ignition OFF, disconnect the harness connector at the K20 Engine Control Module. Test for less than 2 Ω in the low reference circuit end to end. If 2 Ω or greater, repair the open/high resistance in the circuit. If less than 2 Ω, replace the K20 Engine Control Module. If less than 5 Ω Ignition ON. Test for 4.8–5.2 V between the 5 V reference circuit terminal 3 and ground. If less than 4.8 V Ignition OFF, disconnect the harness connector at the K20 Engine Control Module. Test for infinite resistance between the 5 V reference circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 Ω in the 5 V reference circuit end to end. If 2 Ω or greater, repair the open/high resistance in the circuit. If less than 2 Ω, replace the K20 Engine Control Module. If greater than 5.2 V Ignition OFF, disconnect the harness connector at the K20 Engine Control Module, ignition ON. Test for less than 1 V between the 5 V reference circuit and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K20 Engine Control Module. If between 4.8–5.2 V Verify the scan tool Fuel Tank Pressure parameter is less than 0.2 V. If 0.2 V or greater Ignition OFF, disconnect the harness connector at the K20 Engine Control Module, ignition ON Test for less than 1 V between the signal circuit terminal 1 and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the K20 Engine Control Module. If less than 0.2 V Install a 3 A fused jumper wire between the signal circuit terminal 1 and the 5 V reference circuit terminal 3. Verify the scan tool Fuel Tank Pressure Sensor parameter is greater than 4.7 V. If 4.7 V or less Ignition OFF, disconnect the harness connector at the K20 Engine Control Module. Test for infinite resistance between the signal circuit terminal 1 and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 Ω in the signal circuit end to end. If 2 Ω or greater, repair the open/high resistance in the circuit. If less than 2 Ω, replace the K20 Engine Control Module. If greater than 4.7 V Test or replace the B150 Fuel Tank Pressure Sensor.

I would inspect the wiring carefully and thoroughly, check the connectors and pins. I would suspect a wiring fault preventing voltage to the injector before I would suspect a PCM fault. gmupfitter has wiring diagrams to reference.

The fuel tank pressure sensor measures vapor pressure or vacuum in the evaporative emission (EVAP) system. The engine control module (ECM) supplies a 5 V reference and a low reference circuit to the fuel tank pressure sensor. The fuel tank pressure sensor signal voltage varies depending on EVAP system pressure or vacuum. The control module also uses this fuel tank pressure signal to determine atmospheric pressure for use in the engine-off small leak test, DTC P0442. Before using this signal as an atmospheric reference it must first be re-zeroed. Conditions for Running the DTC P0451 DTC P0451 runs only when the engine-off natural vacuum small leak test, P0442, executes. The number of times this test runs can range from 0–2 per engine-off period. The length of the test can be up to 10 min. P0452 and P0453 DTC P0452 and P0453 run continuously when the ignition is ON. P0454 DTC P0454 runs only when the engine-off natural vacuum small leak test, P0442, executes. This test can run once per engine-off period. The length of the test can be up to 10 min. A refueling event is not detected. A refueling event is confirmed if the fuel level has a persistent change of 10% for 30 s during a 10 min refueling rationality test. Conditions for Setting the DTC P0451 This DTC will set if the controller is unable to re-zero the fuel tank pressure sensor voltage within a calibrated range during the engine-off small leak test, P0442. The ECM must complete several engine off natural vacuum test tests before the diagnostic can turn the MIL ON or OFF. P0452 The fuel tank pressure sensor voltage is less than 0.15 V for greater than 10 s. P0453 The fuel tank pressure sensor voltage is more than 4.85 V for greater than 10 s. P0454 If, during the engine-off natural vacuum small leak test, P0442, the ECM detects an abrupt fuel tank pressure signal change, other than a refueling event, this DTC will set. An abrupt change is defined as a change of greater than 0.45 in H2O in the span of 1 s but less than 1 in H2O in 12.5 ms. This test must fail twice in three samples to set this DTC. Action Taken When the DTC Sets DTCs P0451 and P0454 are Type A DTCs. DTCs P0452 and P0453 are Type B DTCs. Conditions for Clearing the MIL/DTC DTCs P0451 and P0454 are Type A DTCs. DTCs P0452 and P0453 are Type B DTCs. Diagnostic Aids P0451 and P0454 A restriction in the EVAP canister or vent lines could prevent fuel vapor pressure from bleeding off fast enough. If the vent system cannot bleed off pressure fast enough, the re-zero procedure may not complete successfully, which could cause this code to set. Ensure that the reference port on the fuel tank pressure sensor is unobstructed. An fuel tank pressure sensor that is skewed or does not have a linear transition from low to high may cause this DTC to set. Scan tool Control Functions, snapshot, and plot functions can help detect erratic sensor response. To test the sensor signal under vacuum conditions, use the Quick Snapshot and the Purge/Seal functions to capture data while commanding purge to 20%, then plot the data to look for erratic sensor operation. A similar test can be done for the pressure side of the sensor operation by applying pressure with the GE 41413-A while taking a snapshot.

I would expect more widespread miss fires if that were the case.

Inspect the rear brakes and u-joints.

Inspect the wiring to the MAF sensor.

Curious if the more frequent regens are causing the lower AVERAGE mpgs. I watch my 25 mile average mpgs go from 18-21 down to 10-12 from a regen. The average for a tank is usually 17-18.

https://www.whiteautoandmedia.com/ Sounds like you need to do something else though.

There is a nipple on the bottom of the main wiring harness pass through grommet. Between the steering column and fender. Comes in above the brake pedal and to the left. This is the recommended location, but its not the easiest to use.

My 2007 (GMT-900) reset at some point in its life, probably similar conditions to a dead battery.

I wouldn't even look at the PCM as a potential culprit. You're on the right track - and if memory serves correctly - the cap and rotor style can foul up pretty quick. In any case using plug wires other than AC Delco is a risk. In that generation the engine weren't so sensitive to plugs as the newer ones.

Inspect the previous work. What brand parts were used? Get codes read and post.

What do you want to see?

I bet its just froze shut.

Nope, just a bolt cover. Door panel removal is pretty easy - a youtube video would explain it easiest.

"...the ECM which will prevent the vehicle starter and fuel pump from operating." The starter cranking rules out the factory immobilizer.