Z71 dimming/blinking lights

When I crank my truck up first thing the lights interior and exterior blink or I guess you could say dim in and out. Once the truck runs awhile they seem fine. Could any one tell what this could be, I was thinking either the alternator or battery but I could be wrong. Any suggestions what it could be or what I could test is appreciated.

My 97 Z71 does this to just once then everythings ok right when you crank it up...according to the guage the alt is charging good and it is a newer battery...

i just had this problem with my z71 check and clean
you battery cable ends then check your voltage it should be 14.2 to14.5 with lights & heater on.
you need to also check what amps your altenator
puts out then check that .my battery was good
my altenator ck ok my amps were no good had to replace alt.p.s.cut off truck and load test battery after checking amps. just because the volts look ok
dont mean your alt is good always compare the output of your amps