RPM drop at speed

Merlins Beard

*Beard not included
I have a 1997 Ls automatic and i have owned it for about 15 months the transmission is ok, it slips into 4th a little but once its in gear it drives fine. when i get between 50 and 60 (closer to 60) the rpms drop by about 500 (from about 3000 to 2500) it almost seems like a normal function but im not sure, if i step on the gas harder the rpms will jump by about 500 without shifting and when i let off the gas it drops again. is this normal?
 
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