The pump itself is unserviceable, the only thing you can do is check that the filter bag aint full of crap.
If you had another pump to test on your car, this would eliminate the pump.
Sounds a long shot to me, but its another cause you can score from you list.
Just a stab in the dark from me, does your fuel regulator have a gauge on it ??
Maybe sitting at the wrong pressure, worth a try i`m sure someone round your area can loan you theirs for five minutes.
Marty.