I have a 5-speed 2005 Mustang V6 with 120,000 miles , and I am having trouble with possibly the clutch slipping. Whenever I am cruising down the road and lay on it, the car revs really high before finally going back down and accelerating. The other day I was driving down the expressway at around 75mph when i floored it. The rpms went from 3000 to 5500 then back down t0 around 3000 before it started accelerating. If you have any suggestion on what it might be and how i can go about fixing it, please let me know.