Grinding of starter Pinion Gear

When I attempt to start my truck listed above Platinum Edition, I hear a grinding noise. I purchased a new starter from my local Napa Auto Parts and had the starter replaced by a local shop and the grinding was lessened, but still persisted intermittently. I still used the truck as I could just turn the key off and back on a few times and one of those times it would start. Then a day or so ago I could no longer get the starter to not grind and start the truck. I then replaced the battery with a Gold Duralast 5-year battery and cleaned all the associated contacts to make sure they were sulfite free. It needed replacement anyway as I had it tested and was informed that the Cold Cranking Amps had diminished. I then removed the starter and took it back to the Napa Autoparts where it was purchased. They exchanged it with a new starter of the same type that I installed. I took a picture of the teeth on the flex plate ring gear before I installed the new starter. The same issue is exhibited with grinding on all start attempts. I am beginning to suspect that the teeth on the flex plate ring gear are worn and that requires replacement. I have attached a photo of the teeth and was wondering if this is the proper diagnosis? The teeth don't look too bad to my "untrained" eye.