02 6.15l chevy 3500 van
 

2002 Chevy 3500 diesel van 6.5L with 210000 miles. getting code p0251. I am a carpenter and my van is always fully loaded with all my tools, carry a lot of weight. Last year my van started shutting down while driving. Thanks to you all I replaced the PMD module and not the fuel pump. saved lots of $$$$. Last week I noticed my van started bucking, sometimes it would be hard to start sometimes easy. Bucking while driving and feels like not enough power going up little inclines. 2 days ago getting to a red light the van shut off took a couple of minutes before it started back up. Put in a new fuel filter, new battery and a new PMD just in case. This is my lively hood, my rolling tool box. Any ideas where to start? Anything would greatly be appreciated.