First, that is a Command CV-13 engine instead of a Courage (unless you have swapped engines).
Cleaning out the fuel bowl and blowing some air through the carb does not constitute a thorough carb cleaning.
To effectively clean the carb you need to spray carburetor cleaner through all the holes and passages of the carb and probe all the small holes and passages with a stiff piece of florist's wire or tag wire. After spraying and probing, then you blow out with air.
Click the link below to download your free manual for the Kohler website.

Here is a link that might be useful: Command

Mownie is right on both counts. Don't know why I wrote "Courage," instead of "Command." Drove into town and got a carb rebuild kit, pulled the carb, sprayed it, "wired" it, blew it out ... then did it all again. Reinstalled it. The sputtering problem is gone, and I'm not losing as many rpm's, but still drop about 250 rpm when the blades are engaged and the tractor is moving. Had to creep through the weeds over the septic tank field. Machine is usable, but still not running right. Told the wife that I'd go to the Rhome (TX) Deere dealer and buy a new L-series tractor, but she won't hear of it. Need more help. (I HATE to admit defeat by taking it to the shop!) BTW, the blade spindles turn freely; no binding there.

OK, about that fuel filter..................did you replace it with a genuine Kohler brand filter, and the correct Kohler filter for your engine?
Kohlers are finicky about wanting the correct Kohler filter or they might behave badly.
Take the spark plug out and post back the color and appearance of her spark plug (refer to the Kohler manual for hints on that). The report from the spark plug will reveal some info about fuel rate that the engine is being fed.