Actually, if your sled idles OK for a couple minutes, then loads up and slows down, you're really close.
Everything has to be set just perfectly for these sleds to idle perfectly for an extended period of time. Usually you have to blip the throttle every so often when the RPMs start to drop.
I hate to say it, but a leaking crank seal can cause the symptoms you're describing, also.
71 degrees in Delphi, Indiana as I type this....unreal. I guess I might as well get the sleds put away for the summer.