I have a 1995 3500 series GMC dump that has the 6.5 turbo that has had some issues in the past.

I had a code pop up out of nowhere saying the optical sensor was bad. Called around and found out the only fix was a new injection pump. Replaced the pump and the truck was 100% again.

About 1 month later and maybe 500 miles of driving, the truck would stall for no reason, no warning signs. It would do it after it was warmed up for a while, say 30 minutes of driving. It would stall while driving, on the gas, off the gas, or at a stop sign or red light. The truck would start right up without hesitation. It does not always stall after 30 minutes or so of driving. Some days, it goes all day without a hitch.

Also changed the fuel/water filter, replaced the lift pump, plus the new injector. When the truck stalls, no lights come on, engine/ brake/ etc. Hooked up the truck to our Snap On diagnostic computer and cannot find any hidden codes.

Oh, the injector came with new gaskets and a new moduale (the piece that looks like a pack of cigarettes with the heat sink)

Any ideas????

The "module" you mention is the PMD (Pump mounted driver). If you left it on it's stock location (mounted to the injection pump) it's all but gauranteed based on the explanation of your issues that it's the issue.

It's quite a common issue with the 6.5 as this unit fails due to heat. The fact it happens only after the engine has warmed up is another telltale of a failing PMD.

You'll want to get it fixed ASAP as it will eventually fail completely and strand you.

Search for "relocate PMD" here in the 6.5 forum and you will find lots of posts on the subject, most importantly adding a heatsink to the PMD and getting it out of the engine compartment completely if possible.

The good news is that all you'll need to probably 100% remedy your issues instantly will be a new PMD. Depending on how you look at it, that could also be the bad news. :)

New from a supporting vendor here they are about $200. Used, on eBay, about $50 or so.

Invest in a heatsink and an extension and get it out of the engine compartment.

Never buy the "used but good" PMD. Remember, once a cookie is burnt you can never return it to a good cookie.

Never buy the "used but good" PMD. Remember, once a cookie is burnt you can never return it to a good cookie.

I bought one a few months back on eBay ($40) and it's been perfect.

I agree you could be hit and miss but most PMD sellers on eBay also warranty their PMD's...so reading feedback is important.

Even if you buy 2 (to have one in the glove box as a spare) it's still quite cheap.

Warranty remaining on new pump (& driver) if that is the problem ?