I'm not sure why you have to "try one more time". I agree with you.
I did NOT change suspension parts to cure vibration. The ONLY exception was the front lower control arms, and that may not even be considered a vibration. It was a thumping/vibration that occurred at lower frequency than vehicle speed, and replacing those parts cured THAT problem, and I haven't experienced anything like it since.
Tranny behavior is getting worse and will be replaced. Whether or not it makes my vibration go away is secondary to having a solid, good working tranny.
One question Larry - can you say one way or another if tire balance can cause an intermittant vibration? (assuming wheel weights are NOT flying around on the rim). I've always believed tire balance is either good or bad, it ain't intermittant.