Volvo MD2020 fuel starvation issues?

[inspectr]

Sitting on the mooring in Double Bay Sydney on Sunday, engine fast idling at around 1500RPM.
Large motor boat charges past at well over the 8 knots no wake limit and the boat violently rolls a few times, 30 seconds later the engine drops revs, coughs a couple of times but returns to normal
I bring the throttle back to idle, then run up to 2500 RPM, drop back, engage forwards and reverse and give the throttle a burst, no problems
30 Minutes later shut down normally
Fuel guage is reading 30% full BTW, but could be stuck - first item to check
4 days later the riggers pick the boat up and report that the engine reduced revs a few times on the way to the repair berth, but resumed normally
Mast out and under repair, they try to get the engine started to bring the boat back to the mooring could not get the engine to rev more than 500 - 800rpm, so we arrange a tow and wait for the mechanic.
These things always happen on the eve of a holiday weekend for me!
I've had the exhaust elbow choke problem that caused similar problems 4 years ago.
I'm thinking that the violent rocking shaken up some sediment / crap in the bottom of the fuel tank and might have clogged a filter on the supply side of the fuel pump
My fuel shutoff pull cable is very stiff, I'm wondering whether the shutoff valve may be loose and not fully open?
We are going to check and top up the fuel tank to 90% full as a first step

Any other suggestions - much appreciated

[Cowpoos]

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