Kohler 13hp Courage loses power under load
Kohler 13hp Courage in Deere STX-38. New plug, air & gas filter, good fuel flow. No-load speed 3325 RPM. Engage mower deck, RPM drops about 200, put tractor in gear & start moving causes another 100 - 150 RPM loss. Occasional sputter from time to time, but not consistent. Cleaned fuel bowl, blew out carb with compressed air, no improvement. What should I try next? Under threat from wife, as this is HER tractor - gotta get it going. She doesn't want a new one, she wants HER tractor fixed! HELP!