That's the exact pump I'm using and relay harness as well but I got the quadstar filter relocation kit running whatever filter they send with it lol and I finally got a set of glow shift gauges I'm much happier with them lol and 14psi with a hx35 is perfect and intercooling it is a great idea big time. Tuning wise quadstar is the only way to go and yessir my original exhaust set up was a custom 4"down pipe and 4" straight pipe it sounded better than a super60 and much cheaper lol

Have you checked fuel pressure?

No, could that be an issue? What do I need to check that>@@dieselnation555

Unfortunately surging on a 6.5L can be caused by a multitude of issues. I would first recommend installing some fuel rated clear/see through tubing, on the fuel return line coming off the Injector pump! A steady stream of bubbles or foam will indicate a leak in your fuel system. Or unfortunately worse, a worn out injector pump! Then I'd verify all the ground points are clean and secure. Then I would try a replacement PMD (pump mounted driver), and/or harness. The coolant temp Sensor can fail causing weird behavior. The advance stepper motor on the injection pump can get stuck, causing issues (it's external). After that, diagnostics get more intense.

I live right on the coast it has its ups and downs thats for sure lol