the highend will affect the low end but it shouldnt be that bad. your idle is way to rich (it always is from the factory) try turning it in 1+ turns until you notics that your idle speed starts to drop. once it starts to level out let it idle for 15 seconds then gun it to full throttle, if it studers then goes your a little rich, if it stops then goes to full your a little lean, this can also happen if you are way to rich.