Nothing is ever easy with these cars. For some reason, my wife's new windows 8 box would not do the "discover new hardware" bit so that I could load the USB driver for the S&S ECU software. I fussed around for about an hour wishing that this stuff ran on a Mac in native mood and then I tried her old win 7 machine and it all came together. I had two fault codes (P0170 and P0172) which are readings for the right and left fuel injection adaptive maps being "maxed out". According to the S&S manual, these fine tune the injection system and smooth things out.
This makes sense from the point of view that the fuel pump motor sounds marginal and I get a fuel pressure reading of 22 psi instead of the 58 psi the S&S shop manual says I should be seeing. The adaptive function just can't quite make up for a missing 36 psi.
Long story short, I ordered a new fuel pump from my dealer. In the mean time, I'll make a stiff drink, position a folding chair in just the right position and gaze admiringly at the fine British coachwork!!