Why does my dash lights and headlights flicker when I go past 60 miles an hour

What is your question?

My truck is a 2003 gmc Sierra 1500 and last night driving on highway past 60 65 mph my head lights and dash lights flicker.

What makes this problem better or worse?

During the elictic thing in truck like windows etc

How long has your 2003 GMC Sierra 1500 had this problem?

Last few years