'86 Westy

I have been driving my van for a week now since it came back form the body
shop.  This morning I get about 100 meters down the road and the tach goes
to zero then back up, then to zero and I get a wicked bucking going on.

I waited till it was warm, same thing.

I check plugs, rotor, cap, plugs.....cleaned them, same thing

Checked the fuel filter (the one before the fuel pump, clear plastic),
completely filthy...ah-hah. The fuel filter was loaded with sand, I'm
thinking that the body shop removed the fuel cap and surround, then
blasted and sanded the van.  Change it out, go for a drive, the bucking is
still there but less severe and less often.  Would some of that sanding
dust have gotten past the pump and into the high pressure fuel filter?
Should I change that one out too?

Or, am I chasing ghosts and I should check the hall sensor as others have
mentioned?

Thanks

Gregor