Transmission problems after drain and fill

I have a 2002 sonata gls v6 with 156,000 miles. I bought it at 152,000 miles and it has ran pretty solid. I figured to change the fluids since i didnt know the history of the vehicle, and the tranny was a little slugish shifting when it was cold. I drained 5 quarts(about) and put in 5 quarts. The first day or two it ran the same as before and then it wouldnt shift past 25mph... the rpms will rise to 4,000 in second gear like its stuck in 2nd. And a loud noticeable clunk at about 3,000 rpms. I dont want to push it so i stay at 20mph , a mechanic friend of mine said i filled it to much according to the dipstick and since theres codes but no codes for tranny(for o2 sensor). I drained about 1 quart and then nothing was on the dipstick, so i put about half quart of the same stuff back in to get some on the stick. Car still runs crappy. Any ideas? When i drained the 5 quarts it was warm so since fluid expands it may have been really 4.5quarts(cold) and i put in 5 quarts of new fluid (cold) which may have expanded to over fill the tranny.

 

Most likely it is. I would check it after it is at operating temp. Then if it is over just open the drain bolt on the transmission and bleed out half a quart. Did you use fluid for the Asian cars? Also worse case scenario the transmission is toast. Get it rebuilt or find one from another 2002-2005 Hyundai Sonata.