installed new pressure switch, low pressure seems like tanks are not filling

two weeks ago installed a new pressure switch, emptied holding tanks refilled with 28PSI switch is registering 50 and dropping when water is turned on, seems like
holding tanks are not filling? Is this electrical or something else, what should I check next?

That sounds normal to me. Expect the pressure to rise after the pressure drops to 30 PSI. The expect the pressure to rise back to 50, and the pump to kick off. At that point, the tanks are full again.

This presumes a 30-50 PSI pressure switch.

Bladder tanks hold so little water that it is hard to tell by feel if they are full or not. Let the tank fill until the pump shuts off, then measure in a bucket how many gallons you get out of a faucet before the pump restarts. That number along with the size of tank and we can tell you if it is working properly.