First off I'd never use that Lucas crap. Second, since you already changed the filter and fluid it could just be you need a new tranny. But since you only dropped the pan to change the filter that was only 3 quarts of the 12, or is it 9, I don't recall right now, that's in the system. I'd change ALL the fluid which includes what's in the torque converter then go from there. There are several write-up's including what I've posted that tells you how to do that. BTW those auto parts house guy’s know just enough to be dangerous.