Power loss

Scan for codes. Being a diesel I suspect clogged air and fuel filters. High mileage cars may have a worn out injector pump. Your timing belt may have jumped a cog or two making it run really bad.

Even though it is a diesel there is still a thing called limp mode. It’s basically when ever you aren’t getting sufficient power based to voltage loss or things like a misfire in the engine. When you try to excelerate do you notice any lights flicker or headlights may be dim