I have complained about an intermittent bucking issue. At the start of this week I swapped in a used fuel pump and what do you know, the issue went from intermittently happing on logging roads to happening on city roads. So I checked that fuel pump delivery and pressure. Both checked out to spec but when I shut down the engine I noticed fuel pressure dropping like a rock. It should hold, specs in Bentley. I started up engine again, pressure up, engine off, pressure now held. Strange eh? Then instead of starting engine I jumped the fuel pump relay so I could be at the gauge. Sometimes pressure held, sometimes it didn't. Pinching off return hose stopped pressure drop. No fuel leakage from vacuum hose to intake. 

I took a chance and guessed that the little ball valve in the FPR was not closing consistently (or perhaps spring was hanging up). I bought a new FPR and now the van runs like it should. All previous issues gone. Been a few days now, but this weekend we're off on a logging road trip so that will be the real test.

alistair