I had the shake down run on my boat. It was an event, but that a different (fun) story.

My transmissions were slipping and I over revved the engines and scrambled the top end of one of my new engines. I not worried about the engines, but I was wondering what the diagnostic procedure would be for checking transmission, u joints, and couplings. Any help would be greatly appreciated.

I have a 1981 33 Cigarette with twin custom 454, Borg Warner Velvet Drive transmissions, and TRS drives.

If you are absolutely sure it was the transmissions slipping than they need to come out and be serviced.You'll have to pull the drives first so you can inspect the u-joints ant couplings then.No way would the u-joints cause slipping and the couplings you would have to spin the splines out for them to slip which is doubtful. Sorry to hear.Are you sure your not blowing the props loose?Are you running rubber hubs that you could have possibly spun? Rubber hubs are only recommended to 370 HP.When I built up my big block I could blow loose the original cleaver I had if I didn't accelerate easy.Sounds unusual both trannys would be slipping.