I am seeking information regarding General McNair replacing General Dockery in brigade command.

Background:

In the Fall of 1863, Brig General Evander McNair was assigned to the command of Brig General Thomas Dockery's infantry brigade.

Questions:

1. Was this due to a previous assignment of General Dockery to the command of the Reserve Corps of Arkansas? And, when was Dockery's reassignment made?
2. If so, was McNair selected simply because he was a convenient replacement?
3. What prompted the reassignment of Dockery? Illness?
4. Was he displaced by McNair by choice of a higher authority?

Here is the time line I have determined [for now]:

9/15 Monticello-Headquarters Churchill’s Division: The two Brigades of Arkansas infantry commanded by Generals Hawthorn and Dockery, respectively, will hereafter report direct to these headquarters
latest reference that indicates Dockery is still commanding his brigade

9/22/64 Kirby Smith to General Greer commanding conscripts...directs that you will order out the Reserve Corps of the State of Arkansas. You will instruct General Dockery that as soon as ready for field service he will report to the district commander for instructions.
First reference to Dockery serving with the Reserve Corps

9/23/64 Headquarters Churchill Division…Special orders…
I. Brigadier General McNair, having been assigned to the command of Arkansas infantry known as Dockery’s brigade….will immediately enter upon the discharge…. as commander of said brigade
Wording implies that McNair's assignment had taken place sometime before this date