Truck Repair: boost pressure, wastegate actuator, dodge 3500

Question
Hello, I have a 99 Dodge 3500 4wd 6cyl cummings engine. The boost used to go to 20psi. The mechanic replaced the fuel filter & the boost sensor in 2005. I was able to bury the gauge at 30 psi. Now it is back to only 20. He replaced the sensor and filter again but it didn't help. Someone said the mechanical aspect of the Watergate is shot and the turbo has be replaced. Any ideas.
I bought the truck used with 91,000 miles. It was modified before I bought it with a 4 in exhaust and supposedly bigger injectors and a bigger turbo.

Thanks very much

Answer
You can just replace the wastegate actuator assy.It will require turbo to be removed to gain access to the wastegate actuator.The bellows usually will rupture & cause low power.Humm,dang mods.Hope there is a turbo part number so you can get just the actuator instead of that $1K turbo.