01 XJ, low or no oil pressure at idle when hot, replaced sending unit, now what?

I just put a new head on my 01 XJ since i bought it with a cracked head. The girl i bought it from said it ran fine before it started overheating. she's a nice girl and i know her, so i don't think she's lying to me.

so when i start it up cold i'm over 40 psi of oil pressure, once it warms up though i'm only at about 15-20 psi cruising and it'll drop to 10, and then sometimes 0 at stop lights.

I don't hear any valvetrain noise. no knocking or anything even when left idling at an indicated 0 psi oil pressure. I had 10/30 synthetic and i changed it over to 20/50 just to see if it would be better and there's no change.

i replaced the sending unit (sensor by the oil filter) but no change. All i did was unscrew the old one and screw in the new one. Someone mentioned cleaning out the hole but i don't think that's the issue.

I'm going to double check with a mechanical gauge and if i see no oil pressure i was going to pull the pan and check the bearings and if they're not down to brass, replace the oil pump.

I was wondering if there's a typical issue that causes this. Is there anything i should be looking for or is this just a powertech motor and i should probably just start motor shopping?

Thanks guys

Its probably something simple. Especially if it seems to run fine.

nevermind I read the entire post

If you're brave and no how to reindex it, pull your camshaft synchronizer and see what the teeth on the gears look like. I think we're about to find a new problem with 00-01s but I'm just starting to get a feel for what's going on.

Definitely verify it with a "mechanical" oil pressure gauge. Gotta have good data to make good decisions. The gauge itself is still in play here, but with that head issue.......it could be real. Damage to the bearings when coolant mixes with the oil due to a cracked 0331 head is not uncommon. If pressure is dangerously low, I would suspect bearings before the oil pump knowing the history of this engine.

Check it with a mechanical gauge like you're thinking.
Where did you buy the sender?