Here's a link to Clemson U. article about St. Augustine grass, which includes a method of dethatching, when & how and aftercare.
I checked Walter Reeves website, but there is one detail that is at variance from all others that discuss dethatching. He states that the blades should be 1" apart, EVERYONE else states; 3" minimum.

Wait until it greens up and have a go!
Rb

Here is a link that might be useful: Controlling thatch in lawn

RB -- Thanks! The only thing I am concerned about is that there are several large patches where some rot occurred late in the season and all of that is dead thatch, that needs to go. If I put down crabgrass preventer now, then I can't dethatch later, because supposedly that will "break the barrier" of the weed preventer.

Grass is a pain. Gorgeous, love it...but it's a pain. Glad I don't have much of it. When I get to the BACK yard, my goal is to have grass in only about 20% of the space.