This is going to sound familiar but here it goes anyway. I put about 200 miles on the last tank of Polar diesel fuel when the engine did the cough sputter and die symptom. Since then I replaced the fuel filter and performed the lift pump test. With the engine running and the T-valve (next to the thermostat housing) open, I get a generous amount of fuel flowing out the drain hose. The behavior of the engine, currently, is very consistent. On cold start-up the motor runs very smooth for about 5 minutes. With the T-valve open the engine continues to run smoothly during this 5 minute period. After that time the engine will cut out momentarily several times and will eventually quit. I am able to re-start the motor for a short period of time after this and if I open the T-valve before the motor stops again I get a good flow of fuel out the T-valve drain line. If I open the valve on top of the fuel filter I think I see a few bubbles come out along with fuel. The fuel looks clean and clear. During this trouble shooting the diesel fuel cap on the fuel tank is loose. I am not sure where to go from here. Could my problem be mechanical, somewhere in the fuel lines or fuel tank. I think I will look at the electrical connection to the IP. Is the fuel solenoid electrical connection a ground connection when the engine is running? I've been riding the bus to work for the last week and I want to start driving my truck again! Thanks, MJ.