I remember talking to Tommy Brandt (Country Gospel Singer) about his Prevost when he set up next to my mear Intruder (It was late due to a flat tire on his towed so I was providing work lights. I have LOTS of work lights)
Noticed two water pump switches. ask him about it
"With both of 'em on it'll knock your hat off in the shower"
(I thought cowboys took their hats off for two things Shower and _____" (Smokey and the Bandit That was Bandit's line)
Seriously. More likely a clogged outlet screen on the water tank or a`clogged inlet screen on the pump. (Outlet screen is optional depending on RV maker, I have one) This will restrict the pump's ability to pump. Also a pinched line, likely the inlet.
If this was a house I'd suspet arterioSclerosis. (Had that on a hot water line in my Sticks and bricks.. A "Grafted" in a new artery (Pipe) and all was good.