Almost Perfect Pitch

Name any song I know and I'll sing it a half step below the actual tonic.
I hear it in my head a half step flat. (A cosmic joke, methinks)

I am playing the mandolin...Grendel, even with the new strings is starting to sound dull.

Temperatures change greatly where I live. A forty degree swing from the low to the high during a day night cycle is not out of the normal course of things.
So the strings on any instrument will stretch and contract with the rise and fall in temperatures.
I check my tuning before I begin...every time. It is a must. I also mean with an expensive strobe tuner, not by ear.
Piano tuners are tuning pairs of strings much like the mandolin. They do not tune the strings to perfect pitch. i.e.A is not set at 440 hz. But the first of the two strings might be at 438 while the upper is at 442.
This intentional dissonance causes the note to ring out. The waves are alternately canceling and then reinforcing each other which makes a slight vibrato effect. Your ear hears sustain.

So that's why the new strings sounded better? They were settling in...moving. I tuned them and after a few minutes had slipped out of tune. I heard notes ringing out and thought it was the new strings!

So the trick I have is to tune the first of the pair a bit sharp and the second a bit flat. A bit is maybe two or three cents (pronounced sonts) at most. Next I should try reversing that, the top flat and the bottom one sharp.
We'll see.