If you only stop the forward motion of the tractor and the engine recovers, it sounds like a fuel related issue. Do as suggested in about 10 of the posts and clean the fuel system and carb. Then adjust the carb and governor while you are at it.
You can find the information in the Kohler manual here:
http://www.onlycubcadets.net/forum/s...ead.php?t=4646
Time the ignition system like this:
http://www.onlycubcadets.net/forum/s...ad.php?t=33461
You can test the coil if you like, but I am pretty sure it's fine:
http://www.onlycubcadets.net/forum/showthread.php?t=11
Take the time and look through the tech section of the forum. Lots of manual, "how to's" and more in it:
http://www.onlycubcadets.net/forum/f...f=19&order=asc
In the Tech section, at the top of the page, you will see another smaller section titled "Tech Tips". Check it out too.