It won't be in there long enough to get varnish. I'm gonna drain it out at 2500 miles. I just can't stand letting it get dark and smelly anymore. Some guys think the HM is a blend. I almost got Pennzoil but that stuff smells like burnt pumpkin seeds.
Check engine mounts. Aftermarkets are stiff and do not last. Check your engine speed, I would think if you have a rough idle, the engine rpm would be wavering.