Hi Jack,
It sounds more like you may be experiencing "current limiting" where your power supply is not providing enough current (amps) to your circuit. Have you checked the voltage before you power everything up and then what the voltage is when the circuit is operating? A schematic of how things are wired would be helpful especially with what parts you are using. An alternate test would be to send fewer characters and there is also the possibility your LCD display is bad? Maybe just send the letters TEST? Flashing and dimming is typically an indication of a power or wiring problem. Best, Ed