Mazda Tribute (Ford Escape) Oil light issues

I recently got a 2002 Mazda Tribute 3.0 V6 with 260,000 miles. The car runs
and shifts like a champ. Starts faster than my 2018! The only issue I had with
it was a very faint oil pressure light flicker at idle in drive only when the AC
was on (I assume because of the lower RPM caused by the compressor). I
decided to do a oil pressure check with a physical gauge. It read 20PSI at
idle in park, and ~14psi in drive. That is within spec for this engine, because I
guess it only wants 11psi at idle! I decided to get a new sending unit. After
installing the new sending unit, I am now getting the oil pressure light to
flicker at idle, and go solid in drive with the AC on. Somehow it got worst with
a new sending unit! I read that the oil light trips at 5-8 PSI. I was getting 15
PSI in drive, so why is the light tripping? Is there something else to look at?
What am I doing wrong here!