I have a 2005 mustang gt 4.6L basically stock. I need help fixing a problem when i shift gears. Starting off the line is fine but shifting into 2nd or 3rd, it's sometimes hard to get it into gear. (Clutch all the way in, foot off the gas) it's like it doesn't let it go into the next gear if I redline it or even get close to red line. What could the problem be? Changed transmission oil about 1000 miles ago...help!!!