1997 4DR 2WD 4.3L V6 Blazer has a problem with grinding when I hit certain sped/rpm combinations. For example ~2,000 RPM at 70MPH in over drive I will feel the whole blazer shake. I'm thinking transmission but not really sure. Anyone have this problem before?

Dropping the blazer into a lower gear or neutral makes the grinding stop immediately. Also accelerateing or taking my foot off the gas will stop the grinding.

Thanks for the help

 

I'd look into a U-joint on the driveshaft first.
Is the symptom a grinding noise, a vibration, or a combination of the two?
So if you are at the speed and rpm with the problem and you accelerate will it go away?

 

Thanks for the suggestion regarding the U-joint. What are signs it needs to be repaired or replaced?

It is more of a vibration now that you ask. The whole vehicle shakes. Accelering or taking my foot of the gas will stop the vibration immediately.

 

Rear U-joint then. Symptoms are what you describe and maybe a howling noise.
It can also be incorrect pinion angle which would happen after the rear axle is removed or leaf springs replaced. If not set correctly following the repairs the same thing can happen.
I had a pinion angle problem with my car and the first time it happened it about took me off the road. Live and learn... 5 degrees of angle can make a big difference.