Changed Transmission Fluid and Filter and now shifts hard?

We have a 2001 Pontiac Grand Am GT, and just changed the transmission fluid and filter. We added Castrol transmission fluid. We measured the fluid we removed and added that amount back in and tried it. It shifted hard. Then we added another 1/2 quart (for spillage and some that was left in the old filter). The car still shifts really hard from 1st to 2nd to 3rd, and when we shift into reverse.

We then did the recommended procedure of making the car level, and taking out the drain plug. We added a little fluid until in drained out of the hole -- so the fluid level was at the bottom of the hole. (We didn't add much, we were pretty close with the first calculation.) The car still shifts hard. Then we added a little more fluid (maybe 3 ounces), and the car still shifts hard.

We want to know if we have too much fluid or too little -- or should we put in some additive? The car was shifting fine before, and this wasn't a big deal to change the fluid and filter. We want to know if we should take fluid out? Add more? What direction do we need to go in? Thanks!

It is a 3.4 L V6 with 80,000 miles on it.