Left side dash light problem

I replaced the dash lights in my 98 Tacoma with four blue LED lights 6 or 7 months ago. Now the far left side by the engine temp and the left side of the tach is dimmer than the rest of the dash. Sometimes I can turn the dimmer knob all the way down and back up to fill brightness and all my dash will be the same brightness but after I drive a bit the left that I mentioned earlier will go back to being dimmer than the rest. As I drive they will get a little brighter then dim again. Not sure what's going on.. They shouldn't be burning out since all the bulbs are the same age..