1998 Chevy S-10 vibration

Have you changed your brake pads recently? Are one of the wheels getting hotter than the rest? Could be a caliper sticking making it difficult for the car to pull until it hits higher rpm's.

I lifted the rear end off the ground both tires turned freely by hand but still vibrated when giving it gas while wheels off the ground at 23 mph

Yes !

I also grabbed a hold of the drive shaft turned it by hand while in neutral, shook it wobbled it, to try and find out if a universal was maybe going bad with no results. With the exception of removing it to see how everything is I can find nothing wrong.
It does seem how-ever that the problem is getting worse very little by little. If I drive it till something shows then there is a good change it will ruin something else but I have no choice but to drive it.
One would think that from years of experiance it would be a universal that what this kind of vibration usually is. One thing I am not to familiar with is this little truck has a two piece drive shaft with a bearing in the middle or actually a little closer to the transmission. But like I said I see nothing wrong, i'm no dummy i've been fixing cars in my driveway for 30 yrs. This is why i've turned to you.