Speculating on the validity of a pump is foolish compared to the relatively easy methods for testing delivery volume and pressure. I might be more concerned with pourous pickup tubes or delivery lines, compromised o-rings, making it difficult for the transfer pump to purge. Maybe try pressurizing the fuel tank gently while idling the engine to isolate wher the problem is on the pickup (suction) side or farther on.
Dirt Cheap
November 2007