I have a 2001 Silverado 2500, crew cab 4wd, short bed. I recently had a one peice drive shaft made from aluminum. Now I have a fine vibration that's strongest at 50mph. It goes away after 60. How the hell do I get rid that? It drives me crazy. Its not ridiculous, just extremely annoying.

 

I wonder how you can tell it's the driveshaft. Anyway if you're sure, then you need to get it balanced.

 

If you did not have the problem before the new shaft, then I have to agree with @mountainmanjoe and pull the shaft and have the balance rechecked.

 

I have a 2000 Silverado 1500 4 wd. I had the same issue and it was the U Joint.
Also, pop the cover off the rear differential and check the teeth on the gears. I found the one I have had previously been rebuilt and the lazy person who put it together left the washers off behind the satellite gears.

Be careful with that drive shaft. I didn't correct my vibration in time and the U joint at the rear end came off. The shaft bounced under the truck while I was running 70 mph. Now, I am having a hard time locating a replacement drive shaft. So, be careful letting that vibration go unchecked.