Help.

[JohnDoe]

Hello there, I'm brand new to the forum and basically here bc I'm desperate for help. I have an 07 Yukon with the 5.3 in which the hydraulic lifters recently went bad and were replaced (replaced bc i figured I'm not keeping it beyond this year). After the replacement i have some rough idling and am getting a p0521 code which i believe is a low oil pressure code even though my cluster gauge is reading just under 40(35ish maybe). Can anyone help me figure out what the problem is? I'm brand new to this and i should mention that a mechanic swapped them not me. I'm taking it back to him in the next few days but I'd like to be a little more informed so i don't get taken for a loop. Thanks in advance!!

[dsr611]