1995 Chevy Astro 1995 Astro Conversion Shakes at high speed

Hello, I have a 1995 Majestic Astro conversion van. About a year ago I noticed that the front end was shaking quite badly. This seemed to happen when driving on regular roads and while on freeways. At that time I replaced all of the following:

1. 4 New tires
2. All new steering linkages, tie rods, etc.
3. Front end alignment
4. Front wheel bearings
5. New front brakes, fluid, and bled

After I had completed everything, it seemed to smooth out for the most part. About a month later I found out I had tightened the wheel bearings in too tight, and I ended up having to have a mechanic replace them. He also replaced the front passenger axle, since the bearing had welded itself onto the shaft! When it was all done, while it wasn't 100% shake free, it was close to 98%. It had very minor vibrations while on the freeway, but not enough to worry about. I drove it this way for about 4 months and then I parked it for about 6 months to save on gas.

Fast forward to now. A few weeks ago I started driving it daily again. It seems that the shake is back, and almost as bad as it was before all of the repairs were done. It appears to start acting up as I get up to about 60+ mph. The faster I go, the worse it gets. At slower speeds, it seems to be ok. I usually drive at about 65mph with the cruise set. The shaking comes and goes, and happens on smooth and rough roads. At times, it almost feels like the van is floating. I have made sure the tires are all still good and that I have the correct tire pressure. I have also climbed underneath and verified all the steering components are tight, and I re-lubed them as well.

Does anyone have any other suggestions as to what I can try next? I am at a loss! Thanks so much!