Thanks so much for your reply. Since my grandfather died on or around Nov. 21. 1864, then at least the fact that the entire 28th was at Camp Magruder narrows down the place that he most probably died. I will surely get your book.
I did get an email from Alan Thompson who told me that there is a record of hospital lists at the National Archives, Record Group 109 and that he has seen mention of a General Hospital at Shreveport, hospital list from Jan 1, 1864 - June 12 1865. Now, I think I'll pursue those hospital lists and see what I can come up with and also try and find an Adjutant General's list for that time period. If I find anything of interest, I'll post it here.
I also think it would be nice to try and learn more about those soldiers who are buried at the Old City Cemetery in Minden. Perhaps they can be identified in general or something.
Again, thanks very much for your help.

Penny Myers