Just added a new back tire to my 08 Roadking. We decided to go for a ride in the interstate. We live in NM so there are some monster hills. On particularly bigs hills, I couldn't gain speed. I have always been able to hit the throttle and gain speed. This time however I could only maintain speed and had to down shift to speed up. The question is, could a new rear tire cause this, or is there another problem?