Well I got the new chip in and fired it up. I had a mostly black picture with a few distorted horizontal bars that also had vertical bars through them. Then after a minute or two the picture popped up and looked normal, if a tiny bit blurry. I turned it off and back on to see if it did the same thing again, but this time the picture stayed extremely distorted. So I put the old chip back in. I get a somewhat watchable picture but about 8-10 thick horizontal bars with color distortion. I've swapped them out again with the same results.
I have seen everywhere that with Toshiba TVs a "distorted mosaic picture" may indicate that you need to replace the formatting board as well. But it doesn't say with Mitsubishi. So I'm trying to figure out if the issue is the formatter board or the color wheel, or where to go next. I don't want to have to replace this TV yet! I could even provide pictures if that helps.