2004 VW new Beetle

Last week took my 2004 VWnew beetle in for repair at Pep Boys. They did a diagnositc test ($100) and put in new coil pack, plug wires and spark plugs. Last month took my car in for new water pump, hoses. Now car has upper end rattle from top of engine and the traction control light comes on when you try to open it up on the highway. It is sluggish when entering the highway and when going up hills. This is new. Even mechanic who fixed it last week says this, he drove it to see for himself. But he doesn't know what is wrong with it. Says it might be valve noise, collapsed lifter or cam shaft. I have no idea what these things are or how much they are and I have already spent $2000 in repairs in 5 weeks. He suggested I take it to a Volkswagen dealer.