Yea I figured it might be the shifters or the RD. Was leaning towards the RD since I used the exact same setup with a different RD with 0 issues before it was transferred here. That said I only previously used it indexed. Not sure I understand what you mean by what controls tension. Would that not be the attachment bolt with the D ring? I had a quick look when I re-installed the new cable and it seemed like it would be risky to get into the mechanism so I left it as is for the time being. I could try going super tight but I am worried I might strip threads or break something. It is tight to the point of being painful on the thumbs and not moving any further.

If anyone knows a guide to disassembling these shifters it would be appreciated. VeloBase.com - Component: SunTour Superbe Pro (6, 7 index)