First thing I would look for is some way to double-check the gauge, freshly rebuilt or not. The line to the gauge might be clogged, too (especially the flexible section near the firewall).
Next thought would be a problem with the pressure relief valve in the oil filter head.
Then I'd probably drop the pan, and check out the oil pump. Last time it happened to me, the oil pump had sucked a bit of swarf through a tear in the screen, and sheared off the tang on the oil pump driveshaft. There have also been some replacement pumps that come apart internally.