2001 GMC lights flicker

I have a 2001 GMC Sierra, I just put a new battery and alternator on in the past 8 months, my problem is when the headlights are on at night, they flicker every now and then, and sometimes I notice my amp meter gauge dropping down for a moment then back up. I have checked all the connections on the battery and alternator, they are tight and clean, so not sure???

Check both ends of both battery cables. Also check the ground for the head lights.

//2000CAYukon

Thanks, I wil try that