I use synthetic in everything. The first time I used it I put Diesel rated Mobil 1 in a VW fox with 250,000 miles. You would not believe the sludge that came out of that motor and it had mostly 5000 mile changes. I am using the Shell Rotella T synthetic in my TDI as my mechanic uses it in his.
You should be able to go to a longer oil drain with the synthetic. With a Diesel you get too much soot and ultimately would need a bypass filter to take advantage of really long drains.
I had installed a bypass on my Jetta and was doing 25,000 mile drains before somebody ran a stop sign & totalled it for me.
Are you running a PTO on your NPR?