QTR-Quadtone RIP

>I'm using a 2200 with the MIS UT3D inks with Eboni installed. ...

>I'd like to be able to use the Costco Glossy too but without 
>swapping the black for PK.

The UT-3D M-position ink is a version of PKN.  
See http://www.paulroark.com/BW-Info/UT-3D_Readme.pdf at page 5.

> I've managed to get the LAB B tone about correct from 0 to about 65 
> but then it dips

As it should if you started to use lots of the PKN (3D-M).  See the graphs
on the page noted above.

> and then goes way up. 

That sound like you have 3D-C coming into the mix.  (If the glossy gets very
dull, it could also be Eboni getting into the act.)

Paul
www.PaulRoark.com