I just bought a 2001 SLK230 and it has not been taken care of. On my first highway drive I was pulling 4000 rpms at 60mph. Thought that was high. Then the next day I took it out again and was pulling around 2200 rpms at 60mph. Much better. Then after taking off from a red light it went back to 4000 at 60mph. Did the transmission reset and it was back to 2200 until taking off from another red light awhile later. Any idea what is happening? I'm stumped.