If I had $1,000 for every guitar I have sold because it didn't stay in tune / perform as required I'd be a lot richer. The problem can take many forms but an often forgetter issue is the machine head seating. My new Suhr would not stay 100% in tune after tremolo use or bending and it really stumped me. I changed strings, lubricated the nut, balanced the action / springs .... Finally a few days later I noticed a tiny gap on a few tuners at the headstock - so I got a large spanner to tighten the machine head on its hole - voila !!! -