Add some Hotshot's Secret to the oil and some of their Firepower fuel treat ( only 7.50 or so a bottle )
Hot Shot's Secret | Diesel Engine Oil Additive
I have run this stuff in the trucks I drive and it flat works ( Mercedes Benz MBE900 and 4000 powered Freightliners and Volvo VED 12 powered Volvo ). Fuel economy went up, engine smoothed out, throttle response got better.
They have a combination specific for the VW TDIs that you should try out. You won't regret it.