you should replace the green seal around the fuel pump case if your going in throught the rear seat. the original seal it difficult to reused because it loses it shape and it too large once removed.
the problem i had was not with the pump at all. it was the filter attached to the pump inside the fuel pump case. i was unable to find a new fuel pump filter without buying an complete assembley for $225
i bought a fsvt pump pump and cleaned my filter but i still had problems i ended up sticking a metal L shaped clip off a writing pen and that allowed the filter to not suck itself close under acceration which was the problem all along.
fyi the fuel pump filter that comes with the fsvt pump is unuseable because of a different design. you must also slighty modify the electrical connection that connects to the fuel pump. its easy enough to do.
i've had to play with the fuel pump at least 15 times before i got it right. i'm now the fuel pump replacement master !
-toss the round disk with the cross. its pretty much useless . and has nothing to do with why your having fuel pump problems above 4k rpms.