Both of the custom driveshafts I've run on my truck were built by Inland Empire Driveline. The first one was 3.5" aluminum with a slipyoke for the overdrive. The second one is all and slipned for use with a fixed yoke on the overdrive.

My fuel cut-off is 128mph. I've been there on both of those driveshafts with no vibration at all. That's running 29.4" tires and the 4.56:1 gears - OVER 6670 RPM!

They build a quality product.