I just traded my trusty 1987 johnson 140 for a 99 dt150. The motor runs great, starts and idles fine. It will pull 5K rpm with the throttle level in the water. However with the shift lever I. Can only reach 1200 rpm max. One time the motor ran rough and I was able to get on plane and pull 4100 rpm. That lasted a short time and it went back to 1200 max. No warning lights, no buzzers. Please help.