Thanks for the reply.
As for the tranny fix fluid, I already have Dr Tranny Shudder Fixx running through the tranny right now from when I was trying to fix a different shudder I had before, due to a carrier bearing needing to be shimmed (fixed it). In light of this I don't want to add anymore friction modifiers or quick fixes, nor do I think that they would help since the first one isn't doing much in there.
As for the filter: I just changed the filter and fluid to Amsoil synthetic about 1-2 months ago, so that wouldn't be the source of my problem.
I guess I'll have to take it in to be looked at... Somehow I don't think its transmission related because the shake seems to continue after I put the tranny in neutral and coast down a hill. Thanks for the tip. Still looking for suggestions.