Well obviously something is not right, best thing to do is changing the drive kit for a fresh new one first and then see if these problems are eliminated, if not you need to have your brake pads checked and all calipers / pads / pistons stripped cleaned and refitted all of which is really routine maintenance, these things don't fix themselves.

You'd feel a knackered chain for sure and you'd hear it too..

Try coasting at speed and check both brakes independently for performance and check as soon as you stop that both wheels spin freely with warm/hot brakes.

A good soaking with GT85/WD40 should give an immediate improvement if it's the C&S..

Bear in mind though that WD40 is a degreaser as well as lubricator. It'll clean up and lube your chain initially but could also wash out the grease behind the o-rings. Still, if your chain is knackered it's not such an issue.

The chain vibes can be annoying but at least you know it's the chain and nothing worse. It's also annoying that the front sprocket doesn't have a separate dampener that can be used with a non-OEM sprocket like Suzuki used on their DR's (OEM XT one with built in dampener is about �50!!)