Cp3 issue maybe?
 

Last couple days my floor it pump has been struggling to hold 19-20k, any ideas of anything to check?

Is your rail capped? Possibly a leaking relief valve.

yep, it's capped, it's not making any oil, and the supply pressure is good

The only sure way I know to figure it out is to hook it up to a DRB and see what actual RP vs command RP is.This will eliminate the possibility of the gauge or the RP sensor being off.Outside of some internal failure on the pump the fca is the only other thing I could see causing it.

the fca did stick once right after i put the pump on when it was new, but i shut it down and all has been well, till now at least

Wouldn't it throw a code if the demanded vs. actual was different?

no it wont. my truck in in need of new injectors. It will command for 21k but only go to 12.5k max at WOT with no programmers on. No codes

def an fca issue, it stuck on the way home tonite...shut it down n fired it back up and now it runs like a rapped ape with all my pressure back. Kind of crazy

FCA'a are some touchy parts! I had one that would randomly up the RP to max while driving at a set speed for prolonged periods of time.Would never do it in stop and go travel or short stents on the interstate.I keep a spare one in my truck now!

you have any surging issues with yours?

I am having similar issue with mine. My rail pressure is all over the place. It will be cruising at 15K to 20K and then the pressure will drop to 3K or bury the gauge way past 30K. Replacing the FCA (arson) and hope it fixes it. Although I think it may be a gauge issue. It will hold past 30K with the stock relief or the capped valve.