Did you actually flush ALL Of the fluid out by disco'ing the tranny cooler output line and pumping it out with the engine running and tranny in neutral while adding fresh ATF+4 from the top? Or did you just drop the tranny pan? If you just dropped the tranny pan, you drained less than half of the contaminated ATF that is inside the tranny and torque converter.
Besides, you actually need to flush it with fresh ATF, not just drain and refill, which can take 20 to 30 quarts of ATF to finally get all of the contaminated ATF out. I'd get it to a shop that can do a complete tranny flush IMMEDIATELY and have it flushed and refilled with fresh ATF+4.
You can't wait to do this, water can actually disolve the glue that holds some of the friction clutches on inside the tranny.