Well in reality you likely increased arrow speed by getting rid of that tubing but the difference SHOULDN'T be enough to cause spine problems....but that doesn't mean it didn't. I have learned that tiny tweaks reap big rewards, or major hassles in archery. My first thought is that your peep is positioned a little different that the previous one. It has been my experience that you have to set this type of peep about a 1/2" higher in the string the the vertical tube type and the horizontal peeps a little lower. You may be a little out of your usual form "finding" your peep and this can make you torque the bow or at least mess up the follow thru. Make sure you are in you normal comfortable form. One other thought is that your peep size may be significantly different. For whatever reason I would guess that you aren't looking through the same plane as before.
Hope this helps... If not I am sure someone else has seen this issue too.

Dave