Stalling Volvo

I have an 86 Volvo 240 DL Station Wagon which I love. It will be running just fine and for no apparent reason loses power and stalls. We have already had both fuel pumps replaced. Didn’t improve the situation. Only change – the fuel gauge no longer works. Took it to a Volvo specialist. He adjusted fuel relays/loose wire to fuel pump. It still stalls. Just on a hunch we took it in to Transmission specialist (Automatic). After a test drive he declared no problem – except of course the now broken tail light from where he backed into one of his own trucks. At one point we thought it had something to do with the amount of gas in the tank as the stalling occurs mostly when it is either full or getting low. However that’s not even completely consistent. Any suggestions?