I would say do compresion test.

Idk where to get A compression tester at

im not shure the best place. i did se a cheap tester at harbor freight, but i dont always like there tools. i would ask some cummins guys what comp should be.

went to harbor frieght about 2 weeks ago but the tester dont work on cummins, it works for almost everything else though

The overflow valve ended up helping a little, but it had air in the system, I'm going to clean my 370's put dv's in it and advance the timing in the near future, I'll post what it does after that