If you got it to connect at 9600 baud then your OBD device must be set to communicate at 9600 baud. The data sheet should tell you how to set it to higher baud rates, then you'll have to select that baud rate in my software.
The instantaneous MPG is just that...MPG at that instant. If you are moving pretty fast then take your foot off the accelerator the value should spike fairly large because you are using very little fuel to go a given distance. It does get averaged by an FIR (moving average) filter, but expect that number to fluctuate. The total and trip MPG should find a steady state value the more you use the software.
