UAalltheway

Please excuse the question, but I'm fairly new to AA.

I'm looking at booking a MCI-JAX 'direct' flight (flt. 2006; 1-stop) on Jan 1st. A couple questions:
- Does this mean the aircraft will be the same on MCI-DFW and DFW-JAX?
- If it is the same aircraft, what are AA policies on staying on the aircraft, etc. for the 40 minute ground time?
- If purchased as a direct flight and trying to upgrade, to both segments have to clear in order for the upgrade to go through? (And also, am I only charged the 500'ers for MCI-JAX instead of MCI-DFW-JAX?)

Thank you!!