To check reg pressure you use the Dye Pressure Tester. The gun should have come with one brand new I believe. Set you reg per the manual. Clean and relube your bolt completely. Check for any broken oring or shredded bumpers. If the gun is brand new, its going to need some paint through it to break everything thing in. The FPS issue should settle out.
Dye makes an spacer skit for the NT11. That's what's going to help you fine tune your efficiency.
Honestly the easiest thing to do, and where you should always start is: (and this goes for any marker)
1. Clean/Inspect/Relube/Replace all Orings and moving parts.
2. Reset Reg pressure and dwell to factory settings.
3. Report back