Acceleration

'97 Mazda Protege about 80K miles, standard shift. Starts fine, never dies (a real champion despite some abusive dirvers). But now it will not climb hills (even in first if starting on a hill) and does not accelerate properly (quite bad at times), and loses power on the go. It also has had a smell at times (like a belt burning). I thought perhaps it was the clutch, repairman drove it and says the clutch is fine. They are now recommending changing the timing belt. From reading your site I am not so sure. Looks like you only say timing belt if it is dying too. In other lack of acceleration questions you note fuel and/or oxygen problems to check. How do we "check" first to make sure it is the timing belt? How do we know the right thing to do?