I have a new to me 99 Baja 302 Boss with twin 454 Mag MPIs turning Mirage Plus 25s. Idling it sounds and feels perfect. In and out of the water (on a hose). Took it around the lake for a couple hours everything was as it should be. Stopped to float for a little bit, when we began to take off the boat shuddered, is the best way to describe it. I backed off the throttles and the shudder stopped. Tried it again and it acted just fine. Nothing else remarkable that day. A week later idled out of the channel into the bay began to take off and the starboard engine shuddered horribly. It felt like a displaced u joint, it was that bad. I backed off and idled the rest of the short trip.
I have removed the out drives and the u joints seem to be in 100% condition (the dealer said all maintenance was done but I was skeptical). The prop hubs are not new. And that is on the list to change.

Does anyone have any suggestions as to what I should be looking for?

Thanks in advance.

Sounds like maybe a drive coupler getting ready to go have you ever smelled rubber burning?

No smells, but I will take a look in the morning. Any thoughts on the best way to do that? Thanks

If you can reach around and feel if the rubber is pushed out or torn. If not a mirror and a flashlight.

Ok, thanks a lot.

Sure one of your props isnt messed up?

Also, pull the props and make sure an old dock line isnt wrapped around the shaft.

The props are in good condition. No lines or any foreign material around the shafts. The hubs seem to be a little loose but I intend to replace them soon.
Could .015" clearance between the hub insert and spline adaptor cause the above condition?

This happened to me on my prop hub . I think it's called flo torq . If you have one make sure the plastic shim things are there. Mine did same thing and I had one on it replaced all four and never did it again. Just a thought

Did you try running only your port or starboard side in gear at a time to try an isolate your condition?

I did attempt to isolate the problem. No luck that way, everything seemed to be OK.
Although I was able to I visually inspect the starboard coupler through the gimbal bearing. I can see a definite delineation where the rubber meets the metal insert.

Now I am going to attempt to change the coupler without pulling the motor out. Fun fun!!
I really appreciate the input!