To properly deal with control of that tranny you WIL have to get involved with the vaccum controls.
You may schmoose over the problem by making it shift real early with the cable adjustment, but the reason you are getting different shifts warm is that you have more foot it it cold giving greater modulator pressure due to less vacuum at similar power levels.
To get a better (longer) explanation go here:
http://www.continentalimports.com/ser_ic20242.html