96 Oil Pressure Problem

I have a 1996 LT4 and the oil pressure guage now reads zero at idle after the car's warmed up. It's normal once I come off idle. This is a new "feature".
The dealer did a manual pressure check and my actual oil pressure is normal at all operating ranges.
I have replaced the pressure sensor and still have the same problem.
Does anyone have any ideas?
Also, if it's the guage itself, how hard is it to get at it?
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