Reduced Engine Power Mode on '03 Burb

[MASTERBrian]

For about 3 years I've been dealing with this issue on our 2003 Suburban with 5.3L Flex Fuel . I've gotten about any and every engine code from this and I've read the service bulletins and such, but the issue keeps popping up.

So far, what I've done in order as best as I can recall...
1) Cleaned Throttle Body, Related Sensors, etc, helped but issue returned in about month or two.
2) Replaced the Throttle Body with an A1 Cardone, as it's what I could locally get. Problem went away immediately and stayed away for several months.
3) Replaced Pigtail at TB and soldered each connection and used heat shrink tape to help water proof and protect. Also used Di-electric grease at fittlings.
4) Replaced Hood to firewall ground strap, unhooked and cleaned the ground strap on Left side of engine to frame(?), same for both ground straps under driver door on frame. Maybe one other ground point, I forget, it's been two years for this, but they were all cleaned, inspected and I used Di-electric grease at each connection to help seal out moisture, etc.
5) Couldn't easily get to the straps on rear of heads, so took to shop and they inspected each of these grounds and said everything looked good on them. I believe they then fogged the system to do a deep clean of the intake and TB....this step as well as grounds might actually have been done before 1st TB replacement.
6) Got codes pointing to throttle position sensor at pedal. I replaced that. Again, this helped for a couple of months.
7) more codes, pointing to TPS at TB. I had the A1 Cardone TB warrantied out for another unit. Actually tried to get refund, but they refused said needed to try another one first. Issue went away until this spring. That was last fall or late summer.
8) started happening again, more codes, etc and this time the truck started actually stalling out at times. Found an AC Delco TB on Amazon and ordered that....locally those seem hard to find and I've had good luck on Amazon with parts and they are fast with Prime Shipping. **ACDelco 217-2293 GM Original Equipment Fuel Injection Throttle Body with Throttle Actuator** This was done in mid-late May.
9) in the last few days the issue is creeping back in. Today I stopped at a shop I use that is heavy into GM engines and spoke with them about possible flash of PCM. The Tech, whom is the son of the Owner and slated to take over the business and seems very knowledgeable, said that since the codes seem to go away within a drive or two that it's most likely NOT the PCM and more than likely in the TB and because I haven't bought one from a GM parts department. His belief is that not all AC Delco's are created equal.

My question is this, can anyone confirm or deny that if I bought an AC Delco from Amazon that it might be different than if I had bought from a GM Dealer. Does it also seem likely that if the code goes away that it would in fact be the TB and NOT the PCM? When I did the pigtail at the TB the wires ended up a bit longer than I would like, but I left them. I'm thinking of now going back and shortening them to be 100% certain there isn't a fault in there, but I highly doubt it. I've also read one guy said he was about in the same boat as me and finally just replaced a ground at the head that looked good and issue seems to be staying away.

I've asked somewhere about replacing these grounds and I believe there are 2-4 on the back of the head....2 on driver side and 1-2 on passenger side. They are a nightmare to get a wrench on, from what I've noticed, which is why I paid the shop to inspect and hopefully replace. I'm debating taking it to an electrical repair shop to see if they can check and replace the grounds as well as the other issues with voltage, but afraid I'll be throwing hundreds down the drain. I've also considered just figuring out what those grounds go to and duplicating them elsewhere on the block. ie....if it goes from head to frame, just pick up an easier to access spot on head and frame and run a completely new strap. Some have suggested that might work and I should leave the old in tact as well.

Any suggestions here? I'm going to call a guy in a few that flashes PCM's to see what he says. Might try that as well.