Have you implemented the configPRE_SLEEP_PROCESSING function?
Here is an example:
void K66F_EnterStopMode(uint32_t* xModifiableIdleTime)
*xModifiableIdleTime = 0;
This would put the system into VLPS mode, you just need to make sure you have a wakeup method enabled before you put it to sleep.
For putting KL27 into deep sleep mode, please refer to the power manager demo.
We have a Have you tried the tickless demo, does this demo serve your purpose?