Flying on southwest tomorrow worried about checking new guitar What is the best is the best way to transport it would I be able to take it on the plane and stow it overhead?

It really depends on each particular airline and how their aircraft are configured. Some overhead compartments are long with no dividers between compartments, so your guitar would fit. Other compartments are segmented in shorter lengths and it might not fit. I would think your best bet would be to take it to the aircraft and try to fit it in (if they'll let you) and if not, then you can gate check it, which means they will take it from you at the gate and walk it down to the baggage compartment. It will be returned to you as you walk off the aircraft. Believe it or not, baggage handlers don't really try to destroy your checked baggage...it just seems that way.