There were several "expeditions" late in the war by Union Cavalry and sometime even Infantry from Pine Bluff towards Monticello. Monticello was an important crossroads at the time. You might do a search in the online Official Records of the War of the Rebellion.

I believe that you will find a few reports on these expeditions in the O.R.'s. One of them may give you a lead to some of the Shirmishes around the Monticello and/or the engagements on the Pine Bluff to Monticello Road. One of the problems is going to be in identifing why your man from the 3rd Louisiana Cavalry was in the Monticello area. He may not have been there because of any skirmish and may have die of reasons other than wounds.