1997 Mercury Marquis 1997 Mercury Grand Marquis shows lean

Periodically, I will be going highway speed and my engine will stall. Accelerating makes the car decelerate even faster. If I pull off the road and let the car idle, sometimes even less than a minute, I have full power and the car accelerates normally, to repeat the frustrating process again in a few minutes.

It has periodically happened since I've owned the car, with varying results on fixes. Here's what I have found out and had done:
1) check engine code says car is running lean
2) had fuel system cleaned by mechanic a couple of years ago, restored power (but it happened again)
3) used more than one injector cleaner recently
4) now it does the same thing when I start the car (rough start, engine coughs and bogs down on acceleration, then catches and accelerates, usually when I let off the accelerator)

Thanks so much for your help!
Mark