1.5 Spacer w/Method Double Standard issue?

So I recently picked up a set of 5 Method Double Standards with 4.75 BS and 0mm offset. I had the Atx Artilleries and liked the look of the 4.5 BS. I wanted to achieve the same with my Double Standards but a friend of mine was getting rid of his brand new 1.5" Hub centric All Pro spacers for his Taco. So I threw them on my wheels. I really like the wider stance, and I've seen guys run a 4.5 BS with 1.25 spacers with no issues, and I'm at the same BS with my set up. After installing them I noticed my suspension stiffened up quite a bit and I get a pretty bad wheel shake now at 45-55 mph. However I stupidly hadn't rotated my tires in almost 20k miles some of those being off road miles. I had my alignment, tire balance, tie rods, and ball joints all checked and they're all good. So my question is, what do you guys think could be causing this issue, everyone is telling me it's the spacers, but I've read differently on here.

 

Have you taken the spacers back off yet to see if the ride softens and the vibes go away? If you haven't, that should be your very next move, as that will definitively answer your question (unlike our opinions).

 

Thats the plan for weekend, Im pretty sure its just the tires. Tons of other guys run the same BS as me with no issues.