First of all, their is NO nitro out there that you can tune once in the morning and then proceed to run all day without having to adjust for changes in temp., humidity, and barometric pressure. Sorry, that's never gonna happen, and if that annoys you then you need to stay away from nitros all together.

I have an MGT 8.0 and I love it!!! I've heard the 4.6's do have tranny issues, but as you said, this can be remedied by putting an FOC in it. You can also find an 8.0 tranny new on ebay(between $50-100) and install that. Those trannies are real tough since EVERYTHING internal is steel. I've had no problems with my diffs either, but people do say you should shim them. I'm just being lazy about it. Only things I'm breaking on my MGT are the body mounts. Otherwise, it's bulletproof!