My boss has a 99 Dodge Ram 2500 5.9L, he told me the other day it started BUCKING or felt like it was going to DIE (stall) - like it was starving for fuel. and I test drove it and couldn't get it to do it. This has happened to him a quite a few times within the last few days (maybe a week) he says it does it around 38-40 mph.

Any susggestions?

Sounds like a fuel delivery problem to me also. I would hook up a fuel pressure gauge to the engine and tape it to the windshield. When it starts acting up, look at the fuel pressure for drop. That's how I check these "intermittant" problems.

Well, the truck on has 39,000 miles on it and it's not constant, it's done it a few times but it will only buck 1-3 times then it straightens up and runs fine.

Change the fuel filter. It's due.

Well this FUEL FILTER is part of the FUEL PUMP MODULE. It is not a standard inline Fuel Filter

Regulator/filter is on top of the module and is replaceable. It isn't easy but it can be done. Drop the tank down a little to give you more room and don't let the fuel line from the pump get away from you when you take it loose.

I was also told the filter was part of the pump and discovered what jpb53 did.