Tuning question for the gurus...

Got a new Jammin X-1 truggy with the Ofna Force .28 motor. I seem to be having a problem holding a steady temp. Broke in fine, leaned out the high end needle a little, bottom end was loading up so I leaned the low speed needle out a little also. Got a good idle, and great power throughout with nice trail of smoke. But after about 4-5 minutes, the temp starts slowly creeping up past 250. If I don't back off, it will keep on creeping up. The highest it got before I shut it down was about 285-290. I tried richening the high speed but I lost a bunch of throttle response. Air leak maybe? Kind of trying to figure this one out.