Running down cause of vibration on belt sander

The motor and VFD direct drive was plan A, but due to wiring issue in the garage, I went with the step pulleys. Once I got some electrician to look at pictures of the panel, I saw it wasn't expensive to get the 240V outlet installed. 12/3 Romex, 240V plug, some wire for the plug to VFD and 12/4 SOOW VFD to motor. We found the panel had a 240V breaker already in it that was not being used, so it was done in about 5-10 minutes, including running/stapling the wire, mounting and testing the outlet!
 
I am experiencing a weird issue on my new belt sander. I have an Ameribrade Fastback, running it with a motor (1725rpm) in a cross slide vise and step pulley/pillow block/driveshaft arrangement. I have a 1 3/4" pulley on the motor and a 2, 3, 4, 5 step pulley on the drive shaft itself (KMG 14" precision ground). The belt sander and the cross slide vise are both mounted to 2x10's, so it's got a nice, thick heavy base, the heavy vise, motor and belt sander. Running it this way works great, 4 speeds (~1400-600 roughly), smooth, little vibration, etc. I can use the vise to get good tension on the adjustable v belt and to line up the pulleys. Whole machine runs pretty smooth. Worked great on some rehandles I just did!

When I put a 5" pulley (and another 2, 3, 4 step pulley I tried yesterday to see if it was the 5" pulley) on the motor end, I get a wicked vibration where the whole assembly wants to walk off the bench. I get the same vibration even at the 5" to 5" and 4" to 5" speeds, which is just a bit over what the fastest speed is with the 4 speed setup that has none of the vibration, since both are nearly 1:1 ratios.

When I touch the pillow block when its running with the 4 speed setup, not much vibration. When I use the 2,3,4 or 5" pulley, the pillow block closest to the step pulley has a lot of vibration and when I press down on it, it lessens, but still has a ton of vibration. I am guessing the pillow block may be bad? Is there any way to check this out? Anything else I should check out? Stumped why a few hundred RPM's more would cause massive vibration or if it's a bad bearing, why it wouldn't be effected at the slightly slower speed? I checked and made sure all of the screws are tight, too. Could the bearing in the pillow block be slightly out of alignment or something?

Video of running the 1.75" to 2" pulley:

Nice and smooth. But once I go to a different pulley on the motor (5" and 2, 3, 4 step pulley), it starts buzzing and walking all over the bench! Should I try a new pulley in case the 2 I have are bent or really out of balance??
Here's a youtube clip, that cracked up myself & my son,go find it its a classic have a look st where the belt is and watch it go !Screenshot_20210403-192419_YouTube.jpg
 
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