Gas gauge goes UP when I press the pedal???

My fuel gauge has been inconsistent ever since I bought the car. When the ignition is turned on, the needle will rise to the correct fuel level, but will "stutter" on its way, and sometimes randomly quit working during the drive. I installed a new sending unit when I swapped 5/16" for 3/8" lines, and the gauge's performance improved. I haven't gotten under the dash to look at the wiring, because quite frankly, I hate working under the dash and I'm procrastinating.

However, I noticed something odd yesterday while driving down the interstate.

I noticed that when I let off the gas pedal, the gauge would go down. Almost to the point of disappearing past "E". Then when I press the accelerator, the gauge goes back up. I could repeat this quite consistently. What is happening here? How on earth is this even possible? I made a video of this, and I'll share it once I can get it uploaded on the Tube.

'74 Barracuda with a rallye cluster.

-----LOL , MINE HAS ALWAYS GONE DOWN WHEN i HIT THE LOUD PEDAL !!