Dave, the fact that the track wasn't being prep could be the whole issue. I went a few weeks back on a Friday night, lost about 1/2 second. Came back the following Saturday and I was right where I expected.
My Super comp buddy always tells me, then reinforces that you don't make changes or tune based on a bad outting, only on a good one. Meaning don't chase things that aren't there, exspecially when you know the track wasn't up to speed.
I ran Monroe gas shocks then converted to Comp Eng. drg shocks in the rear, saw no diff. The combination change that you made, very minor, should not have caused massive wheelspin, the poor track surface would.
Here's a couple pics for ya'll 
