2003 Prius/MPG dropped after transaxle fluid change

Hi i being on forums reading on how to do the transaxle fluid change and finally did it myself. I dropped and clean the pan and put new gasket. The MPG dropped a little, I was getting 44.6 before fluid change and after fluid change it dropped to 43.3 any ideas why this happened.

car has 82,000 miles

I might of overfilled because i only took about 4 1/2 qts and i put in all 5 of type IV..

Please advised,

Thank You