ISX15 2350 oil pressure acting strange

So we switched out oil filter and cut it open. Looked pretty good. Some very fine particles (assuming from all the new parts) and then we tried hooking it up to a trailer. Same problem. Runs 40ish at 200F down the highway. Hits 212ish F and it drops off to 28-30. When it drops below 210 and I stop...it'll be back up to 40+ until it hits 212 again. Driving me crazy
We're gonna try hooking up a mechanical gauge this week and try it again. It's going in for an injector replacement this week.

 

Yeah...it's working and KW says as long as it's over 20psi on highway with the "new style" oil pump that it's fine. That just seems so low to me. The whole point of shimming it was to have a little higher psi.
And it's just so strange that it drops off drastically like that (12-14psi) when it hits 212F.

 

Sorry...the shimming I'm talking about is adding a few dimes to your oil pump to increase pressure. Lots of guys are doing it and I did it on another truck when we rebuilt and it works good for getting pressures to stay around 40-42 running down the highways.
They say the newer style pumps without shimming will run at about 30-32 (hwy) and idle about 18

 

Can't say for sure. We ended up putting a different oil pump in and haven't seen a problem since. Not sure if it was the shims causing the problem or the pump itself was a problem.
I did buy a mechanical oil pressure gauge to hook up and compare but by the time it showed up the mail...the pump had been changed out.
It still makes no sense that it was only doing it after it would hit a certain temperature. But that's all I can tell you....wish I could be more help for you