Calling all old schoolers.......

Not really relevant but I had the same problem 40 years ago with an old London taxi and couldn't find the cause so I sold it cheap. Buyer found a ball of wool in the tank that would be sucked into and block the pipe then when it died and suction stopped would float out again.
Also had a pinto engined ford that acted similar, I never found that problem either. Sometimes I was certain it was electrical others it was fuelling, I never really forgave ford for all that misery tbh.

 

My guess is trash in the tank. It builds on on the pickup sock then, when you turn it off it dissipates. Run it again and it clogs the pick up sock. Would happen more while under load than just sitting idle.

Seen it before. Especially on a motor home that sits.

I’m sure they didn’t clean the inside of the tank while they had the pump out?

 

I stopped buying ethanol gas for everything that does not run on a regular basis. That helped a lot.

 

Have you checked your catalytic convertor?