sleep mode in pic16f1618/19
Almost certainly one or more of your I/O pins are sourcing current.  The pin drivers are still on during sleep.  If you want the pins to be high impedance during sleep, you have to explicitly set them that way.

Put the processor to sleep and look at all the pin voltages.  For any that are high, examine the circuit carefully to see if keeping that line high requires current.

Some peripherals continue to draw power during sleep.  For the lowest power consumption, make sure things like the watchdog timer, brownout detect, and the like are off.  However, 6.6 mA is a lot for a few peripherals on during sleep.  The real problem is pins set high sourcing current, as described above.