Air compresser

[the missing link]

So first things first , I am not a mechanic , I can not spell worth a dam or type,and I am far from knowing much .
I have been having issues with my air system ( 871 isx ) .it started with my air dryer ,it would purge when the compresser would kick in then out and would air up ( only under high boost ). And eventually got worse so I did order one ,i know I had to replace it anyway , not a big deal , I just had a run of horrible luck and pushed further then I should of .
So it got worse before I got back to town (leaking air when the governor was out , so I said the hell with it and bypassed it . Worked like a hot dam for about a day and then get worse again in and out , losing air when the governer was out . Then it would not kick out so I figured I stop for the night and put a governer on in the morning .
Morning come and I put a governer on , I figured I had it fixed , fired up the truck , it went to 135 psi before it kicked out , I swear ,kicked the tires and started trouble shooting everything .
I hooked the dryer back up , switched lines , tested lines, I did everything. Meanwhile while this all is going on its kicking in and out all the time within 10 secs at times ( not losing any air presser in the tanks ).
So at my wits ends found the dirty word ( shop ) and limped it in . First rate guys I got to say .
So we went though everything again and again , changed governer again ,tried bypassing the dryer , everything .
So the only thing we can come up with is the compresser ( unloaded valve ). Which in cummins mind makes more since to have in the dam compresser unstead of outside on the top. Why would you change a 20 dollar valve when you can change a 1700 $ compresser .
By the way I just greased my truck / steering shaft before this , so my arms were full of grease , like I said very smart I am .....
Little bit more info with the dryer bypassed the compresser will not kick out
With the dryer hooked up it will relieve the extra presser
With shop air hooked up , the dryer will purge when the governer kicks out ,but the compresser keeps a ticking

So like I said the only thing we are smart enough to come up with is the unloaded valve is screwed . The lent me a van , I drove 1 hour to pick the compresser up tonight . Tomorrow I know if that's the problem .
It's been a long dam day
Any knowledge would be appreciated
With kept everybody updated
Thanks