Jeep Cherokee Forum - Help me diagnose culprit of low oil pressure at hot idle, 2001 cherokee sport

I have a 2001 cherokee sport. A couple years back my engine overheated. Following this, I replaced the cooling system with a brand new radiator, thermostat, and hoses. I noticed my oil pressure slowly began to drop to zero when the engine was at running temp while idling. For a short time it didn't seem to drop completely to zero, but eventually it began dropping completely to zero at warm idle, but would rise when I accelerated. I never noticed any loud knocking while this would happen, but still worried about possible damage. In order to prevent damage I would lightly throttle it while holding the brake while stopped at a red light, this way I was able to prevent psi dropping to zero and the "check gauges" light from turning on. First I tried a thicker 50w oil, this defiantly delayed the time and speed for the oil pressure to drop to zero, it wouldn't drop as fast when stopped and took more time after starting the engine for the low pressure problem to begin, but eventually it would still drop to zero at idle, especially on hot days. Next we replaced the sending unit, no luck. Then the oil pump was replaced, no luck. Then After learning about the "0331 Tuppy Head cracking issue", I removed the oil cap and looked down into the top of the engine to discover it was in fact cracked, between cylinders 3 and 4. So I replaced the cracked head with a brand new head I purchased from odessa cylinder(formerly clearwater cylinder), to end up with the same "oil pressure dropping to zero at warm idle" problem. Now recently we began checking bearing clearances, so far all connecting rod bearing clearances are within allowable spec range, clearance on connecting rod bearings 1-6 =(0.002"-0.00175"). Regarding the main bearings(MainBear-1=0.0175") (MB-2=0.0016") (MB-3=0.0015")(MB-4=0.0015")(MB-5=0.0019")(MB-6=0.00175"). So now what?! This is about to send me to the psych tank....Again!!! What else could it be?