This might explain the problem I had the other day with mine, I went round a long bend at full chat and the car coughed and chugged so I let off and got scared and drove it home off boost!
It was under 1/4 of tank though, never had it happen before but I've never really given it full beans on a low tank before...

I'm also looking for an MFI tank Roger, I get fed up of dropping the tank to check the pump!