Once you have the maps saved to your SD card I would pull the card from the phone so your maps aren't deleted then uninstall the app, power down and restart the phone, re-install the app, power off the phone, install SD card then power up the phone. This should remove all the app stuff and maps on your phone then re-install a fresh app and basically clean things up.
To speed up your phone while in the field turn off WIFI, your mobile data and clean the phones memory cash.
To speed up your phone while in the field turn off WIFI, your mobile data and clean the phones memory cash.