what is the most likely probable fault
Reply #1 –
Sure you have enough tranny fluid in there?
Valvebody might be gummed up somewhere...if it just starts slipping out of nowhere but under acceleration it grabs gears good...it's losing fluid pressure and releasing clutch packs/bands until the pressure comes back. Either fluid sloshes away from the pickup/filter is plugged up/VB has an issue somewhere that's starving it of pressure/flow.
I feel like this is one of those instances of operating very close to a high/low threshold of the "process window" as people say at work...and just the right conditions push you over the edge into -ville.
The buzzing is the TV spring (or maybe just the actual valve itself). I have to look back at my Baumann shift kit manual, the word from them is that it's a resonant vibration that builds and causes that noise. The spring they supply you gets rid of it for good.