tamper mode? "02" envoy

my 2002 envoy is having similar issue's i've read about in previous post about passlock. i changed the battery one day when it would not start, five year old battery, reasonable conclusion. so in the morning the car would not start, come home from work then it would start. starting to get angry now. so after checking all connections, testing relay, testing starter, i noticed the security light flashing, is the car in a tamper mode? i also read about bypassing pk2, but does this apply to my vehicle? need a little help here. also why will it start one time and not the other????:confused:

Google or site search the pk11 or 111 relearn procedure.

Google or site search the pk11 or 111 relearn procedure.
thank you maxwedge,, i will do that