I just bought a new American Standard Cadet III toilet. I installed it
myself, using a wax ring with a plastic horn. For some reason it does
not flush well. I played with the flapper chain and water level float,
and even when I get a full flush with flapper up during full flush, it
seems to flush slowly. When the bowl is full, I always require several
flushes to get the stuff down.
I even tried to use a pail, to flush down solids and it required two
pails full.

I don't remember having any problems with the previous toilet. The only
reason I changed the toilet was because my wife wanted it to match the
color of the new bathtub.

What could the problem be? Before removing toilet, could the wax seal
even be a possible cause? (incorrect seal between the wax ring and
toilet). I don't see any leaking.

The bathtub which uses the same waste pipe (about 5 feet away) seems to
have good drainage, so I can't imagine it being related to a vent
problem.