Constant flickering of TFT Display
Flicker is almost always a timing issue. In theory it's possible it's a wiring issue in the LED, and unstable power can be unpredictable, so check you connections, solder joints, and power supply. Use the shortest cable possible between the screen and whatever it's connected to. If your hardware is good, try and slow down your timing/refresh rates/etc. The Mega doesn't have much in the way of RAM and can easily choke trying to push that many frames of that many pixels per second. It's also worth knowing how you are connecting to the screen, I2C, SPI, etc