I've never heard of the Servomotor cycling at 3800-4000 rpm. Is your sled efi or carb? The carb models cycle once when the sled is first started. Each valve will open and close once. The EFI models don't do this. They don't open until about 6800 rpm to give peak flow and power. The reason they open at 6800rpm and not 4000 rpm is fuel milage. Its figured that anywhere from 4000-6500 rpm should be cruising speed on trails and light snow. I don't know how it affects fuel milage but thats what they are supposed to do. And when you need peak power above 6800 rpm they open and give the engine no restrictions and full flow for more power.
I have never heard of them opening at such low revs.
I would guess if they did the sled would hesitate like crazy.
The motor is built to have more low end power with them closed....and to make top rpm power with them open.
If they opened at say just 4000 rpm i bet it would stumble and bog like crazy.