FT Benz

I got in my 07 E550W4 this morning, started it up, shifted it into gear and started to drive (or at least try to drive). The rpms went up but and it moved forward slowly but it felt like it was in neutral and the gear was not fully engaging. I thought the ebrake was on but it wasn't and I pushed it down and disengaged it anyway. Then I tried it in reverse and the same thing. Engine revved and it moved slowly like it was only slightly engaged. After about a minute and moving around the driveway a bit it went back to normal and was shifting just fine.

By way of background it had not been driven in 4-5 days and the temp this morning was about 45 degrees F. Car has about 57K miles.

Any thoughts? Should I be concerned?