throttle not closing all the way

That's not supposed to happen. It kindof points to the pedal and throttle arm not being synchronized. and that when you floor it you may be overstressing the throttle shaft. Usually this happens when the carb does not have a Mopar adapter on it, or the anchor bracket is too far away from the throttle arm. I know you said you believed MRL had the right parts on there, so I'll shut up now.