If you are going on this trip for a professional reason such as a paid performance or a recording session, then I suggest you buy the guitar it's own seat on the flights. It is a fine musical instrument, not a $30 roll-aboard bag, and it should be transported with the same consideration you would extend to a member of your family. If you can not reasonably justify the expense of buying your guitar it's own seat on the flights, then I suggest that you leave the guitar at home.

According to http://www.delta.com/traveling_check...ryon/index.jsp:
"Carry-on Baggage Size Restrictions
When oversized bags do not fit in the overhead bins, delays occur. Fees will be applied to the oversized bag if it has to be checked at the gate. To avoid delays as well as fees, follow these size requirements:
Baggage may not exceed 45 linear inches (or 115 cm) in combined length, width, and height.
Baggage must fit easily in the Carry-on Baggage Check, which is located near the check-in counters and at the gate and is approximately 22" x 14" x 9" (or 56 x 36 x 23 cm)."