Strange behaviour on trip to Florida

We are just back from a great trip from Pa. to Florida and back but my 08 Prius excibited some strange behavoiur and mpgs. dropped from 48 on way down to only 41 to 42 on way back. (Don't say it's because coming back was uphill LOL). The car ran great about half way down but then I noticed when we pulled off an exit ramp and came to a stop the ICE would continue to run??? No arrows were showing on the display acted like it was warming up when cold?? This did it a couple of times on way down and I noticed when on the highway it would always show grren bars, 1 away from being full. Once we got to Daytona around town it acted normal. Then on the way back there was not one time it ever showed blue like normal, always all green one away from being full, in fact when i got off exit ramps the battery was so full that by the time I coased to a stop at the end of an exit ramp it would be complety full, all green bars and mpg's on way back dropped to 40 to 42 mpgs. I should say the car was really packed and heavy with three of us and tons of luggage you could notice the car sitting down in the rear. I looking to see if you think I might have a problem or if the extra weight could make the car behave this way. Thanks. PS I haven't had time yet to drive the car around in a normal routine yet since we just got back

 

It was pretty warm on the way down and half way back. The first time the ICE kept running when we stopped at traffic light at end of exit ramp and sat for awhile it was in the 70's. Actually when it was colder on the way home the ICE shut off all the time at stops like normal. I'll drive it around here now that we're back like normal and see if it' acts like it always does before I have it checked.

 

No almost positive it always stayed in D. Local drving today my mpg's back up to 48-50 so who knows LOL