04 was first year for the v10tdi in the states… PD motor, they were a bit problematic from what i recall.
06-07 was the next two year run for the v10tdi in the treg but this time it had particulate filters and common rail I THINK but could still be a PD motor.
09-present are v6tdi’s that are pretty good. they have the urea injection but thats only every so often i think 10k? but they are 225hp/425tq. i’ve driven several v6 tdi tregs and they are pretty damn snappy same goes for the q7 tdi’s…
for the 04,06-07 you can get tuners for and get 450-500, 750+tq fwiw