727 slipping

OK, started up the Demon today, got the engine running great, and the trans too...I thought. My combo is a fairly fresh but stock 440 with a new rebuilt 727 lockup trans. Its the first time the trans has been used since the rebuild, and I had Frank Lupo make me a 11inch 2400 stall converter for it (and yes its a lockup style converter). At first, the trans did great, then after it got warmed up on the maiden voyage it slowly kept slipping more and more until the revs had to be rediculously high just to get it to move. Trans fluid level is good...checked it with engine running and trans in neutral. Initial adjustment of the kickdown linkage was checked 3 times, although when I got back from the short drive,I checked it again and did have to adjust it some. The adjustment made no difference though, I can put it into gear now and there is no trans pull at least at idle. What am I missing? Is there any thing else that may need adjusted? Is the kickdown supposed to have a spring to keep it pulled forward at the carburator, or does it just rely on trans spring pressure for the forward movement, could that be the problem? Any ideas, please speak up. Thanks