Stoddard, I can highly recommend either Jenny or Tony Vaught, of "For the Horse Ranch" in Fair Play, MO - about 2 hrs from Joplin. They are sensible, consistent, fair, reasonable, and effective. Jenny is a former Parelli trainer, but first and foremost she is a superb horsewoman. They understand trail riding and can get your horse straightened out! I sent my gelding to them, who had some respect and attitude issues and I got back a different (and wonderful) horse. I can't say enough great things about them. PM me if you want more information - they're at www.forthehorse.org.
They specialize in gaited horses, but they own and train other breeds as well - mine was AQHA. I couldn't be happier with what they did for him!