Toyota Repair: Poor MPG with 2005 Toyota Avalon XLS, 2005 toyota avalon, mileage figures

Question
I have been getting 17-19 mpg since my Avalon was new.  EPA gave 22-31 mpg.  I'm retired 65 yr old who babys the car. However,I have never put premium gas in the car.  Toyota says fuel and trans indicators are good.  I do get slippage when I pull down off the street into a parking lot.  Engine races unless I'm careful to soft pedal the gas.  Other times the car seems to surge when I brake but these are more "seat-of-the-pants" impressions.  The trans seems to react inconsistently; for example, it automatically down shifts when I go down a hill and apply the brakes.  But not always.  Toyota says the down shift is intended.  I hoped Toyota would find the problem but they quickly decided that it was operator generated. We've gone 10k with no relief.  Any recommendations?

Answer
First of all the EPA mileage figures are in most cases unrealistic, in the real world the mileage that car owners get are almost always less because of less than ideal and varying driving conditions.
The transmission is computer controlled and upshifting and downshifting of these transmissions can seem abnormal if the driver is not used to this but this is normal, the downshifting going down a hill is also normal, this is designed to use engine braking to slow the car down, finally, if there was any problem with the transmission the on board diagnostic system would turn warning lights on the dash on, also I have checked to see if there are any service bulletins regarding transmission issues from Toyota and there are none.