Tom,

at the risk of saying something you already know....

I wouldn't be looking at the absolute numbers at that fine level of detail.
If all cylinders peak near the same fuel, flow, that's the thing.  I would way have them peak together than have the same temp, if I can only have one.

If all cht's are well below 400, great.

Personally I don't think the quality of the probes and analog circuits is good enough to push really hard on the absolute numbers.
that said, some other ideas:

- does the problem move with the probe or stay with the cylinder?
- are all egt probes exactly the same distance from the cylinder?  same depth into pipe?  same angle into pipe?