There's much good information here.

Here's another thought based on lots of time behind a mic. Monitor speakers are a good thing, but you must be aware of what you're hearing in them. You haven't mentioned whether you're a cappella, or using an instrument, solo or part of a group. If you're on stage with any one/thing else, be sure that sound is well represented in the monitor. That can help your tuning. It makes sense, because we make the best music when we listen to each other.

Best,
Dave