2020 Cascadia DD15 mil light leads one cylinder fails compression test

I drive the truck to a dealer because of mil light on. I got this truck a few months ago and have put on a new coolant pump. I did a compression test when I got it. The result was #1 97%, #2 100%, #3 98%, #4 98%, #5 90%, #6 91%. The truck now has 540,000 miles on it. Below is the diagnosis report today:

PULLED UNIT INTO SHOP CONNECTED DL8 FOUND ACTIVE CODE 5362/16 ENGINE IDLE SMOOTHNESS CONTROL CYLINDER #5 QUANTITY DEFICIT AND CONFIRMED CODE 5359/18 ENGINE IDLE SMOOTHNESS CONTROL CYLINDER #2 QUANTITY DEFICIT.

PERFORMED T/S STEPS 1-10 FOUND FAILING RELATIVE COMPRESSION RESULTS FOR CYLINDER #5 AT 79%. NEXT IS TO PULL VALVE COVER TO INSPECT FOR ANY DAMAGE AND PERFORM OVERHEAD ADJUSTMENT.

WENT AHEAD AND PULLED ENGINE OIL FILTER TO INSPECT FOR METAL SINCE UNIT WAS THROWING CODE FOR 2 CYLINDERS BUT FOUND NO METAL IN OIL FILTER MEDIA AT THIS TIME. REINSTALLED OIL FILTER. CODE RESPONE WILL INDUCE 25% DERATE ON ENGINE.

The shop is closed now and will reopen Monday to continue the diagnosis.

I am now extremely frustrated and feel it is a lemon truck. Please give me some advice on this case. Thank you so much!

 

Sorry hear about this, and thank you for sharing.
Did the shop do a manual compression test(get the actual compression reading other than the relative compression percentage) before working on the engine?

 

From my understanding, this percentage is not an actual compression value. It defines the best compression cylinder as 100%, and compares all other cylinders to the best one, and gives percentages to other cylinders compared to the 100% one.