Okay this thing is driving me nuts. I start the truck
Oil pressure is fine. On dummy gauge and mech gauge
Sits for a few and the bells ding and my gages go to
0.i review it a bit and it comes back up. When driving the mech gauge reads 25 - 30 at 65mph. Come to a stop mech gauge goes back to 0
I've changed the oil pressure switch. On the left side of block.
I have used the pressure switch hole for the mech gauge
And the Allen head hole to the left of the switch.
Trucks stock..When the bells ring before the dummy oil gauge
The cluster reads check gages. But I'm going by the mech gauge only now...

 

At 60-65mph you should be seeing between 70-75 psi of oil pressure. At least that's what my mechanical gauge reads. Oil pressure that low ain't good. Stopped up oil pickup, plugged filter, or worst case scenario, bad bearings at the crank journals. Keep us posted!!

 

If you know for sure your mech gauge is good and it drops to zero, you have problems! I would try a second gauge for piece of mind and if it also goes to zero, stop driving the truck until you are able to figure it out. Some good ideas to start with above.

Good luck man!