I'd probably still experement with the transmission fluid though - we had the same problem in our 2003 Civic Hybrid with 65000 miles. Every time we started the car from a complete stop there was a "lurching" like a slipping clutch.

Switching out the fluid in the CVT seems to have helped smooth over the problem.

 

I've run into this slipping feel after a stop on several different Priuses back when I had Zipcar in Boston, so at least 5 different ones all varying between 1000 or so miles (never was first to a new one) and 20000 miles. I think it really is just a matter of the electric motors switching directions.

I haven't hit it in the Prius I now own since I last posted, but maybe it's because I've been driving these things so long I avoid the hard-stop/hard-go series of events that trigger it.

 

Mike,
I had a similar problem with my 2006. When I read that you had recently installed the after-market EV only switch, that clicked with me. These symptoms began right after I installed that as well. So, I remived it and the symptoms are gone!
I can only surmise from the info posted here that the EV circuit interferes with the operation of the electrical motor somehow. This is NOT a good thing, obviously!
Samuel