my new clutch slips!

[cas3]

beautiful day here yesterday so i thought i could finally put some real miles on my 34 jalopy. its been around the neighborhood a few times, but the first time out on the pavement with insurance. i put about 50 miles on, around the big block i call it, for the most part all good. temp stayed at 180, subaru thermostats, oil pressure a little lower than i expected, but still 30, hot, cruising. columbia works fine, trans is smooth shifting, motor runs perfect, but the fire breathin monster has enough power to break the clutch loose in overdrive/high. a 59ab with merc innards, new fort wayne 9"clutch and pp, early flywheel with the blob cut off, balanced and surfaced. all smooth but if i floor it at highway speed i can get it to break loose. this project has been going on for two years, so at this point i will hope its just some surface rust that will fix itself, time will tell. old photo, she's a little more dressed up now!