mlbex...re: your tuning issues...
when you restrung your mando, did you stretch the strings out as you were putting the new ones on? If not, you may simply be experiencing the strings stretching and settling around the tuner posts.
re: making the set up better... if the action is how you like it, and the intonation is good, what exactly are you looking for?
"Set up" is a general term that refers to a variety of things. Once the basics are in place...clarity, no buzzing, intonation, action, etc...what makes it "outstanding" is how well it's set up for YOU.
Otter OM #1
Brian Dean OM #32
Old Wave Mandola #372
Phoenix Neoclassical #256
If you're gonna walk on thin ice, you might as well dance!