SL-55 Trouble. NEED TECH HELP!!!!!

[SL-FITTY-5]

I own a 2004 SL-55. Has 15,000 miles. Recently when I first start the car and punch it (the pedal to the floor) it HAULS BALLS!!! I can feel myself go back in my own seat. However, when I continue to drive for a while and continually punch it every now and then, all of a sudden it's as if it's riding like a sl-500. I see my revs go up but the speedometer barely moves and I dont feel that G-force like I did when I first steped into the car. It's going literally 0-60 in 7 seconds. I have continually told this to the Mercedes dealership down here in Reno and they continually think i've gone crazy. Please help, if it's a computer problem or a trans. prob. or if you have any info on what's happening. Thanks.