Stalling

I have a 1984 380SL with 75,000 miles. I have had no problems with the car until last week when it began stalling and would be hard to start. I replaced the fuel pump relay but this did nothing to remedy the problem. It occurrs most frequently right after you start the car and put it in gear. it does not matter if the car is hot or cold. Any suggestions as to where I should look now. I plan on replacing the fuel filter to see if this helps. Any help you could give me would be nmuch appreciated.

I would not go to the filter yet, because it does not sound like you are running out of gas. What is the idle rpm? If you increase the rpm with your gas pedel two hundred rpm and then put it in gear, What happens?

replace the starter lockout switch on the transmission.