I’m having an issue with my 1999 Suburban, 5.7 L motor. The truck was purchased in 2005 with 44,000 miles. The intake manifold gasket was replaced as soon as I got her. I recall a misfire/stumble on medium to hard acceleration on hills, but I never was concerned. She now has 157,000 miles on her.
I now would like to find out what the problem is. Over the past year, the trouble code scanned was P304 and P300. Now, it’s only P300. The following have been replaced:

1. Plugs,cap and rotor
2. wires
3. EGR valve
4. MAF sensor
5. Both cat converters
6. camshaft sensor
7. crankshaft position sensor
8. New all-metal distributor
9. coil
10.ignition control module
11. Fuel pump
12. New style MPFI system replacing the often problematic spider injectors.
13. Fuel filter

The truck is STILL stumbling under load on hills under hard acceleration. It runs and idles normally the rest of the time. When the stumbling starts, the check engine light flashes, then stays on for a day or 2 before turning off. The car idles rough for a few minutes before going back to normal.

Can someone shed some light on what this issue could be and how to fix it?
The only thing not replaced yet is the throttle position sensor. What I am thinking is it’s a part that was never replaced or something that was and is defective. Thoughts?

Thank you all in advance!!!