I cannot figure this out - and what's causing it.

Having an issue on Flintstones... The Lower Right Flipper is always perfect, but the upper right and lower left (Seems to happen at the same time) will be fine, then they both get really weak, and then they go back to normal. This has happened several times and will happen several times during the same game. I swapped out the Flipper Opto board in the back with a different one but the weird behavior returned. Game has a new Driver Board in it as well.

Game appears to have new flipper coils in all three flippers. Any help would be greatly appreciated! I'm lost!