2002 Accord LX Coupe Brake Issues

I recently bought a 2002 Accord LX Special Edition 4-cyl 2-dr coupe and
I've been having braking problems with it for 3 months now (it only had
35.5K on it when bought it). They said the brakes in the back were
replaced when I bought it 11/25/05 and they recently replaced the drums
due to my consistent complaining, but its still doing EXACTLY the same
thing - when braking, usually at high speeds, and suddenly, I feel a
grinding in the pedal and a noise/ burning smell. Its scaring the heck
out of me needless to say and I havent gone past 60 MPH on highway. It
doesnt feel like its braking properly or even that it will stop, but it
eventually does. They treat me like the serice loony when I visit and
say its "normal".
Any advice?? Its still under warranty - I even tried to take it to
another service dealer but they turned me away as it is under warranty
to the other dealer!!
Thanks in advance.