I also had a DLP (61" RCA/InFocus).
Yes, the bulb was a continual hassle.
I gave up on it and went LCD. And I had gotten the TV for free.
Feel lucky that your Mitsu doesn't have the plastic lens issue my InFocus did.
The newer bulbs ran hotter (brighter is good, right?), and melted the original lens in the middle of the light engine.
Much Frankenstein later, it worked.
The ballast board that is powering the lamp might be bad. That could take out lamps as well as not light them up well.
You can check
They sell replacement boards and are very helpful.