So I am an active member on Duramax forum and have posted this issue on that site with no suggestions. The truck in question is a 94 6.5 TD 2500 4x4 5 speed (4:10 gears) with an F VIN engine. The truck has 145,000 miles on it and I have installed a Heath Diesel PMD relocate about 6 years ago, a cold air intake, 4" straight pipe exhaust, new injectors at 108,000 and new glow plugs. I also installed a new lift pump about 6 years ago as well.

I have 2 issues with the truck that I have been trying to find an answer for:

1. When I am driving down the road at cruising speed it will occasionally stutter, almost like a quick miss in the motor. this is a split second event just enough to feel the stutter but no dash lights and the gauges don't move when it happens. It doesn't do it all the time only occasionally. I took a 350 mile trip with it not too long ago and I would say it did this about 6 times on the whole trip. Another thing to note is that when the truck is cold started (50F or below), it will smoke and misses like crazy for about 10 seconds. After that, it runs idles flawless and it starts easily every time after.

2. Issue number 2 is especially noticeable when pulling a trailer. What happens is when I hit a hill and I give it more pedal my boost will pick up but then it acts like it defuels then boost goes to almost zero then back up to 10 then back to zero and on and on. I have wired the wastegate shut thinking it was a vacuum issue, but it still does it which makes me believe it is defueling. I also found out that at 2500 rpm the pump will naturally defuel for some odd reason, but this boost surge happens at rpms below 2500 as well. I have read online that it could be a multitude of different things from AI temp sensor, boost sensor, PMD issue, and so on, but I was hoping someone could give me a really good starting point.

Any starting points would be greatly appreciated.