Sorry to revive this old thread but the same thing happened to me. Developed right after mixing the kit and allowing the chemicals to come up to temp. I used the Dynamic Chrome developer diluted 1+1 for 9 mins, as instructed, with constant agitation on a Unicolor motor base. Slides still came out super dark.
I've developed slide film several different times over the years and never had such poor results. It was 4 rolls from 3 different cameras. Film of varying age from 2 - 10 years expired (normally not an issue with slide). The best looking roll out of the lot was the 10-year expired Aerochrome of all things. The rolls from my Nikon point-and-shoot and Yashica TLR (with fresh meter battery) all came out super dark.
Last night I mixed their normal E6 developer to push 2 rolls of Provia to ISO 200. Followed the instructions; diluted the developer in half and followed the time on the sheet. Even added a whole minute for being a few degrees under temp. Still very dark compared to results from other kits. I wonder if it's this whole dilution thing and maybe their timings are off. I really don't know.