Lee,
When I drained my tank and pulled the sending unit, I found a piece of cast aluminum about 1 1/4" long x 1/4" thick semi circle in the bottom of the tank. Don't know what it was or where it came from. Must have been dropped in the tank by PO. Other than that my tank was absolutely clean...not rust. Appears to be a newer tank. I would drain your tank and take the sending unit out and have a look with a flash light. Might me something floating around and clogging the outlet. Needless to say that that piece of cast aluminum would have sooner than later ended up in the tank outlet, reducing the flow.
Tim
