I get it now! And Ive even seen the loop-back on a 5.9 but i never made the connectio. In fact, I forgot all about it! On my DT466 and on some other DD 2 strokers, the return goes all the way to the tank and doesnt loop back in at the filters. Since that was the setup i was thinking of, that is why I couldnt imagine how the two are related. Which is funny because ive even worked on the 5.9 and had to specifically replace a leaking washer on the very banjo fitting where it goes back into the filter!
Thanks for the info! Happy to learn something new today. Now, the question is, why is the OP losing power!? I am very curious to find out. Hopefully it is easy. I also had the thought after re reading his description that maybe his transmission is not holding gears properly and upshifting too early and it might be related to the flywheel job. Maybe there was a modulator cable that was disconnected and not reattached or broke...just thinking out loud!
Patina enthusiast and professional busman