I own an '87 300E with 130K which has recently begun to stall unexpectedly after normal operating temp has been reached. It has never stalled when the engine is cold or is warming up, and has never been difficult to start when cold. It will always start again after several attempts and then will run fine (until the next episode). This happens maybe twice a day, usually in the afteroons with the AC on and the outside temp hot.
I have replaced the fuel pump relay and the overvoltage protection relay in hopes of solving the problem, but it continues. Both fuel pumps and filter were replaced at about 100K. Distributer cap, rotor, coil, plugs were replaced within the last year. The battery seems fully charged.
What could be going on here? Any thoughts would be appreciated.

Thanks