Console has problem playing games

Most games only have stuttering here and there (most notably, Wii Fit U where it freezes and stops recognizing inputs for a few Seconds), but recently I've tried playing some F-Zero games and while the SNES VC was in constant slow speed, the N64 VC was barely playable. Constantly stuttering and stops, it was awful and the Console never did that before!

Since I've bought a new Samsung SSD with 1TB of free space, I tested if that could be the problem; so I moved F-Zero X to my Nand, unplugged the SSD and tried playing it that way. Still the same issues.

I also cleaned the Fan, unplugged every other Accessories and even replaced the Clock Power Cell, in hopes that the problem might lie there somehow. Though, it was of no help...

Now that I've tried everything else, I don't know what could be the culprit... Could it maybe be some Aroma Plugin? Or is it some Hardware failure that needs fixing? I don't know...