That bit about the drive-through at McDonalds sounds like the torque converter to me. Next time it happens, try shifting into N or P and see if it still does it. Seeing as the car has 100k on it and most people are too retarded to think about such things, it probably needs a transmission fluid flush like whoa. Sometimes, but not often, I'll get a similar thing when the AC compressor cycles, so try turning the air conditioning off too.
The slowing-down-on-the-freeway part is normal; with the MZR, if you're coasting the ECU will automatically cut fuel and spark, so you'll start engine braking a little bit right away.
I don't have an MSF account you can post this up there if you want.
