Car runs great regularly, but occasionally loses power while driving. Pulling over for a couple of seconds is typically all it takes to regain power and continue driving. Check engine light typically comes on when this happens, then goes out later. "Mechanic" has replaced fuel pump relay, and both fuel pumps (two separate visits), but problem still persists. I'd appreciate any suggestions as to the source of the problem, as I'm preparing to drop it off for the third visit...