I had vibration under acceleration at 60-75ish mph. That issue is fixed now. The old intermediate shaft bearing had almost zero play in it, same as the new one once it was installed so it probably did nothing. It was only $60 in parts and very easy to change once the axle was out. My original post had a link to a how to but the post wasn't approved by the mods so Google it if you want to see how to do it.
My wheels/tires have a vibration between 65-75 too, they have been balanced a few times. When I swap my RX-8 wheels/tires on it is nice and smooth now. Lighter wheels/tires are next.
Good to hear your vibration is gone I know how annoying that is. Doing coilovers this weekend then after that going to replace my driver axle. I suppose I will skip doing intermediate shaft since mine has no play as well and heeltoe auto also suggested that replacing it wouldn't help. Hopefully after both axles my 20-25 vibration will be gone, but I doubt it will help my 60+ vibration.
Thanks for keeping us updated and I will keep you guys updated as well. Any advice/ideas from new viewers would still be appreciated.