Trans overheats

I have a 70 duster 340 with a 451 big block and my trans overheats . I bought it fully rebuilt manual reverse built for drag racing ,thats what they told me, Im using a frank lupo 8.5 street n strip converter. I have a cooler with fan. Im wondering, Im using B&M synthetic fluid,is that wrong or is it my converter or since im mainly on the street ,something else.

duster 30.jpg