As Jason stated- I would check the fuel pressure regulator. I had a similar issue a couple years ago and after replacing the fuel filter and pump I changed the regulator and it was fixed.

Quick update on my earlier post. I ended up pulling the tank, after draining the ten or so gallons left in the tank.

There is a huge amount of corrosion in the pick up area, probably close to an inch. In addition, there was crud on the inside of the internal filter at the pick up point. I had replaced the fuel lines, but it looks like the old one failed internally based on the amount of rubber crud.

The original problem really seemed like a fuel starvation issue, I am thinking when the car was not under load/at idle, the fuel pump could pull through all the crud, but once it got going, it just couldn't pull past it.

Current plan is to see if the tank can survive being hot tanked at a radiator shop. If it doesn't survive, I'll look got a good/better original tank, or perhaps bite the bullet and look to install a fuel cell (more safety is usually better.....)

Thanks for those that commented and/or reached out! More to follow.....

Bill

I thought the tanks were made out of plastic?? Or is that just on certain model years??

Early tanks (83 and early '84's) were steel. I wish I could just swap in a plastic tank, but the attachment point would require a fair amount of fabrication from what I understand. BTW, I also think the 924S cars (86/87) used steel tanks...

My fuel starvation symptoms due to crap in the tank were different. Initially I replaced the pump, filter and sock. The car ran fine for a whole day but the next I went out and it 'appeared' to run out of gas although I knew that wasnt possible. It would not start and come to find out the fuel pump stopped working. It was new so I got it warrantied. Next track day, I went out and after 2 sessions it started coughing and shuddering and finally died. The pump was extremely hot, at this point I knew something was up with the tank. Pulled out the full sender and the thing was filled with literally a cup of dirt! This is an 86 so no idea how it got in there. It was caking over the sock and burning out the pump. Jacked it up at the track and sprayed it out with the dirty gas. Never had 'that' problem again.