CHECK THE FLUID AGAIN WHEN THE ENGINE IS FULLY WARMED UP TO OPERATING TEMP. WHILE IT'S RUNNING IN PARK . THERE IS AN INTERNAL THERMOSTAT THAT ONLY OPENS AT OPERATING TEMP. WHAT I HAVE SEEN IS THE SHOP DOING THE SERVICE CHECKS THE FLUID AFTER THEY HAVE FILLED THE TRANS. AND IT WILL READ FULL. IF THEY DROVE IT AROUND THE BLOCK AND CHECKED IT AGAIN IT WOULD BE DOWN TWO QTS. ONCE THE THERMO OPENED UP. THE FILTER IS NOT THE PROBLEM, IF IT WAS CLOGGED AT ALL IT WOULD BE EVEN WORSE WHEN WARMED UP AND CREATE A HI PITCHED PUMP WHINE. NOW HERES THE BAD NEWS. IF THE FLUID IS OK THEN YOU HAVE AN INTERNAL PROBLEM. I HAVE SEEN THE RUBBER LIP SEAL INSIDE THE INPUT DRUM SLIGHTLY RIP JUST ENOUGH TO DO THIS EXACT THING MANY TIMES. GOOD LUCK
-GEORGE