It does indeed sound like a fuel delivery issue which Professor G noted with the pump mounted driver, or PMD that is attached to the DB4 injection pump. A number of other things can cause stalling such as low fuel in the tank, restricted fuel filter, weak lift pump, air intrusion in the fuel line, worn injection pump, ultra low sulfer diesel fuel which causes the injection pump to have internal problems.
First thing is to mix 16 ounces of Walmart marine outboard 2 cycle TC-W3 rated oil to a full tank of fuel. You should quickly notice your 6.5l engine running quieter and will solve the problem if it is ULSD related. The next thing is to check lift pump pressure at idle, and higher to see if the lift pump is failing. Always a good idea to replace the primary fuel filter when encountering running issues. Be sure to purchase fuel from a station that sells lots of fuel so you will know the fuel is fresh. Check all the fuel lines for leaks that would also let air in. Check grounds, wiring and connectors for good integrity.
;-)