Rwthomas,
I sense your frustration with the lack of response. Anyway, I do NOT know how to remove said trim piece. The only other piece of trim that I believe is attatched by small nuts through the rear C pillar is the chrome edged piece that is color coordinated with a bit of taper. I "think" that trim is by nuts. Perhaps you know for sure.
Anyway, good luck and know that some of us are indeed out here reading and memorizing this stuff....hahaha
By the way, the back and forth banter concerfning "turbo" and "exhaust" info seemed interesting to me at least. You seem to have TWEAKED your truck pretty well.
Hope that all is well and a CORRECT response to the trim issue is forthcoming!
See you at the GTG..........whenever it may be

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Best wishes always, spo out.