I used to drive a Chevy Aveo automatic trans (rated at 23 city / 31 highway) and on my 11 mile (one way) commute to school I learned that p&g was the best solution. Driving at a constant speed would get me about 29-32 mpg on any given day. Driving with load would give me 31-33 mpg, and finally, p&g would give me 35-44 mpg. I did p&g with putting my car into neutral and it didn't cause any problems, it just raised my mpg substantially. When I accelerated, I was usually able to keep the engine load around 70-80% without causing my car to downshift as long as I was maintaining the right speed. 60-45 mph was the sweet spot range for p&g in my aveo. As long as your car can smoothly shift from neutral to drive when you travel at speed, which I imagine it will, then I highly recommend doing p&g with neutral coasting (engine on, of course).
