2005 Volvo 5.7 GXI fuel issues?

[Havasu bound]

Ran great last fall when test driving. Over the winter we changed fuel filter, put stabilizer in fuel tank. Did a carpet change so everything including one tank had to come out. Put all back together, put in water and under load ran up to 3000rpm then sputtered, backfired. Like starving for fuel. Runs fine at idle. After minute or two it will run back up to 3000 rpm for a minute or two then start the sputtering all over again. Not an engine guy so took to dealer. They put on computer and found no codes. So they put on water to experience issue. They put back on computer and again found no codes. Think it may be "mapes sensor" ( not sure of spelling). Does this make sense? Or should something else be obvious or checked? Guessing is something I do, not sure dealer should be using this route. Any ideas or thoughts? This is a pontoon boat with 190 hours.

[Don S]

Since you had the fuel system apart, I would be more inclined to thing you have a loose hose clamp on a line or a plugged or crimped hose somewhere causing low fuel flow.

[Havasu bound]

Thanks for your input. I wish it would have been loose clamps, plugged vents, kinked lines. Ended up being low pressure fuel pump and of course they say you cant buy just that, you have to buy the whole thing. Throw another thousand at it.

[Pulse8]

DID you check your fuel pump and pressure.
A guy I know had about the same problem, his AFPR was not functioning as should be.

[Havasu bound]

No, I didnt check pressure, the shop did. What is AFPR?
Thank you

[Pulse8]

fuel pressure should be about 34psi if i'm right.

Its the automatic fuel pressure regulator which is vacuüm operated where the delivery and return fuel lines are conected to.
Inside there is a membrame which could be broken so your fuel delivery is limited to some + idle.