Low hot water pressure

Our house is 3 years old, PVC piping. Main supply water pressure is regulated at 50 psi. Pressure at hot water tank drain is 50 psi with all faucets closed, drops to 0-5 psi with any one hot faucet open. Is it a blockage at the tank inlet ???

It could be.
Is the valve on the cold supply to the water heater open all the way?
What happens when you use cold water?

Inlet valve is open all the way. I also opened and closed it several times in case some trash was caught in the ball valve. Cold water is fine. Tank outlet is fine, since pressure drop is measured at the tank drain. I drained about 5 gallons from the tank, didn't help