1997 E320 trans shifting

I bought a 1997 E320 just over a year ago. Just turned 58,000k miles. I've noticed a slight lag when the transmission shifts. Let me explain: when passsing someone if I push accelerator pedal all the way down it seems that the rpms shoot up right away and there is about a 1 second lag before the trans downshifts. Also, when I floor the car from a stop there seems to be the same lag when shifting from 1st to 2nd.