wastegate?
 

We have a 96 or 97 not possitive chevy3500 at work I use as my service truck. Just recently it started to surge kind of it will drop rpms and smoke like crazy for about 10 seconds then quit smoking and take back off. Does it worse towing and going up hills even empty. I work on diesels but used to Cummins and cats. It feels like the waste gate is opening and closing. I'm thinking vaccuum leak or wore out actuator. Any help or ides would be greatly appreciated

make sure your lift pump is running while the engine is?