Ditch the auto now, you are loosing 25% right there. I owned both for many many years, it is simply amazing how much fuel the transmission costs...
Autos should have the 0.154 nozzles and an 11mm pump. Verify, as the years go by someone may have changed stuff-the pump has a bosch id plate with long numbers and the nozzles will have a stamping inside the injector body. Clean the intake, make sure the VNT is working properly on the turbo and good vacuum hoses through out the system. You could get a bigger pump head (12mm) and keep the small nozzles so it really pushes fuel but be aware it will put more stress on the timing belt.
You can run the timing advanced, near the top end of the graph. You might have to play with the timing belt depending on where it is positioned on the injection pump sprocket, sometimes there is not enough range to get it where you want and off a tooth for max timing.
18 years into our automatic tdi, best tank was 750 miles running I-81/66/95 down to Florida 24 hour trip non stop. I drafted, I did not use a/c and kept the windows up just vented with the sunroof. I was never able to repeat it, the next best was usually 650-675 with normal commuting tanks around 550.
With a manual trans I was into 800 easy commuting, higher on trips.
Scangauge or similar bluetooth apps give lots of info like TPS, load, temps, all handy to know for max mpg. We run ours at 1/3 throttle for max mpg.