Piedmont Pottery

Controllers die. When a controller starts having problems it's best to just replace it, especially when it's that old. Often one programming system will die, either the Ramp/Hold or the Cone Fire. Or buttons stop working, etc. One thing to check before you give up on it- is it in a very humid environment? Humidity can cause the circuit board to malfunction. If so, try drying the back of the board with a hair dryer and see if it starts working. Don't overheat it, be gentle. I

Your best bet really is to do an absorption test and find out exactly what that looks like under the firing conditions you want to use. We can tell you all day, but you wouldn’t be the first one of us that need to hold a thing in our hands to truly understand a lesson. 

Have you tried calling M&M Pottery Supply?  They might be the best source of information on this.

Hi Anna!
My guess, the differently coloured pots are thick/thicker - takes longer to reach peak temp, longer to burn out organics, etc.
As for picking up a glaze layer, easy enough to test for difference in absorption. Given that a sufficiently thick layer of glaze is applied, reaching full maturity - the clay, that is - in the glaze fire may be at issue.
The more open pots' inside can "see" the elements better - they get the radiant heat more directly than the enclosed shapes.
Back to thickness, perhaps more time at the critical temps (750, 1050, 1500F) and slow ramp to peak, giving time for thicker parts.
Back to thickness II, if all the ware in a load are not about the same thickness, loading so the thicker ones are in the hotter areas of the kiln should help.
Some air movement - supplying oxygen - is important for thorough bisque.

I am not making wheels to sale but here is a link to a short video of a kick treadle wheel I just finished making from a black locust tree and some hardware.
Tree to Treadle