The high limit is set with full cable tension, adjust the high limit, then pull on the cable on the downtube to make sure it is set correctly. If it doesn't get close to the high limit when upshifting then it is a cable tension issue. If, when you adjust it to adequately shift onto the big ring and it is still rubbing alot in the middle ring, it may be a derailleur alignment issue or you may just have to trim the shifter more often if you have the option. A properly set up triple shouldn't rub in any of the middle ring combos though except for possibly the two extreme ends of the cassette.