Codi Hammar

I recently got into a 93 gmc sierra half ton that I knew was going to need some work. I know that there is a very good chance I will be replacing the alternator. the truck has a really decent 350 motor in it. When i get up to speed the mph guage is glitchy and "twitchy" untill you keep it at a steady speed then it kind of settles in. I also noticed the oil pressure guage and the gas gauge will go into the red untill im almost at a complete stop then they jump back up where they should be.

is the low alternator the cause of this or will I need to replace the entire cluster panel? any tips or ideas are apreciated.