inkdemon

I have a new 12 mustang gt premium. About 500 miles on it,and mostly local driving. What I have noticed the few times out on the hwy, 5th gear shift can be more of a thought process,and more effort than 1-4. Meaning like going into reverse you have to push harder. Is this something that will loosen and break in as I go? All other manual tranny cars I have owned were pre-owned and seemed to slide into the upper gears easily. Also I'm throwing a short shifter on as well. So just wondering if it's just something I have to get used to, or something that will become easy with a break in period. Thanks for any and all comments,and advice.