i have 1990 chevy 1500 silverado reg. cab sportside, 350 v8, auto-trans, i have a vibration in drive trane between 35-45 mph, goes away at lower or higher speeds. has any body had this problem?.

 

Check the U-joints, thay are probably bad. They may feel tight, but usually it is because the rollers are gummed up from the factory (wornout).

 

2000 silverado same problem skippy is right, the u-joints are hard to check for slop sometimes. when replacing the joints get the ones with grease fittings, these will last longer and operate quieter if greased every other oil change.

 

I would check the drive shaft support bearing. I had a situation where the same thing was happening. I replaced the u joints but not the support bearing. It never got better. Then one day I was backing up hard and fast and it felt like I lost the whole rear end. In fact the support bearing had disintegrated. I replaced it and all vibrations went away.

It's always the thing I DON'T replace!