Have you checked for codes? Do so even if the SES light is off.
My first inclination would be to connect a laptop to it and monitor the sensor readings and fuel / spark commands while its running and when it's acting-up. I think this would tell you volumes, instead of throwing parts at it. Now, I understand that sometimes "throwing parts" is the easier route, but replacing parts comes with the risk of screwing something up and introducing
another, new problem.
You mentioned "replaced ground straps that were missing". How do you know they were missing? How do you know you re-installed every one necessary?
Does the vehicle's electrical system show ANY evidence of prior tampering?...
- You mentioned "missing ground straps"
- Are there any loose or obviously new / replaced / disconnected wires elsewhere under the hood?
- (ditto) under the dash or at the base of the steering column?
- has the vehicle been operating in a salty environment that might have lead to connector corrosion? Oceanside? Northern states w/ winter salt?
You could try to swap out the PCM
if you like (I've see your other post here about the PCM
https://www.gmt400.com/threads/flagship-one-pcm.58826/). I would be inclined to try one from a junk yard, provided they can assure you it's for the same engine / trans combo.