If your TC is slipping, the shift kit will make things worse ... it's time for a new TC.
Shameless plug I know, but I have a fully rebuilt CD4E for a V6 that I'm trying to help a friend sell:
http://www.fastcougar.com/forums/messageview.cfm?catid=6&threadid=119886
I did the rebuild myself ... check out the thread. Aside from the shiftkit, the valvebody was completely rebuilt using Sonnax valves.