2001 Volkswagen TDI 2001 Golf TDI is sluggish

I have a 2001 golf TDI that isn't driving as fast as it did when I bought it. When driving in fourth gear and trying to pass someone, you could feel the engine slug down and give up trying; still moving but accelerating very slowly.
I've changed the air filter, fuel filter, and checked all the hoses for the turbo. Found two hoses that were disconnected. One that connects to the vacuum resvoir and one that connects to the air filter compartment at the bottom. When I connected the two hoses, the performance came back and worked great for a day but died again later. Someone please give me more ideas to what I could do to fix it.