Frank, check the chain or connector length from the handle to the flapper; it sounds like the flapper isn't being raised as far as it should be. (too much slack in the chain)
Another possibility is some flappers have a sort of counter-balance on them & it may just be time for a replacement flapper.
Once you get things to where the flapper opens as it should, and the water level in the tank is correct, that comforting "WHOOOOOSH" will return.
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