are you running an o-ring chain?? Did you change the sprockets with the chain last time you changed it?? do you lube the chain before you ride? is it oring or non oring??
a few people have told me that o-ring chains are good but only if they are fully cleaned and lubricated every time you use them, if you dont they cause more friction as they being to seized and you will LOSE power gradualy the more and more it does. they are more expensive and they do stretch. you wont find a chain that doesnt stretch it just like finding tyres that dont wear, you cant! but in my opinion, get a good quality standard link chain no o or x rings, use good quality lube after you wash and before you ride and not only will that save you money it will save it seizing up on you and losing you power, also if you snap it or damage it its cheaper to replace. hope this helps you.