To mturner:
You should have the same 5R55W transmission that I have. That grinding poor shifting you have could be one of two things.
If your grinding noise is heard as you start moving from a stop while turning it is very likely the anti-slip differential. This could be somewhat normal as the differential ages. Not really sure about that, but it is a source for the noise.
Next, the flashing OD light and the gears for your mileage may be due to worn clutch bands. My transmission has more than double the mileage of yours, but I was able to tighten the clutch bands and the OD light has stopped flashing. This could also help with your transmission. If it doesn't it certainly won't hurt. See my LONG post on this on another thread.