I have researched this a little, since its a common 16-mm film. Retrochrome aka ektachrome 2253 is not an E6 film, but VNF-1. Its a quite different process, in particular its first developer. If you process it as E6 it will have a color shift due to this and it will also be a fair bit more washed out and grainy (you can look on youtube for 16mm examples). To process more correctly you should mix your own first developer and make addition to the color developer (it needs benzylalcohol, if i remember correctly).
If you cant do that a solution may be to pull the first developer 1-2 stops, run it at 4 minutes, for example.
Also since its not a "real" e6 film result will never really be comparable, VNF films were cheaper and with thinner emulsion, as far as i know.