I'm guessing you are cruising at about 1500 - 1800 rpm while at 35 - 40 mph?

Thats quite a bit below your stall on a 10" continental. I probably bought my 11" continental from the same re-seller. I like mine...or liked it, when the tranny was working.

That being said, the Continentals are supposed to be tight for normal driving, and flash to stall speed when you stick it. Thats what mine does. Still, I think that is too lose a convertor for your rear end and cam.