Are you using your own E-6 processing to do this slide film? I've done a little E-6 processing in a tank, and actually spent about a year working in a la=b doing C-41 and E-6 processing and am familiar with the process, but if I remember correctly E-6 is very temperature dependent. You can vary the temperature slightly to push or pull the process but you will get some color skewing.
Still nice to see slide photos. It brings back memories.