You know all the symptoms - chain goes slack 10 minutes after you adjust it. Bike seems to surge for no apparent reason. There are extra noises coming from somewhere down there. Driveability at low speeds is not so good. Adjust some more. Tight at one spot, loose elsewhere.
Anyway, had a new chain and sprockets installed today, and what a difference! All of the above have disappeared. Bike feels normal again, and is even more of a joy to ride. Chain: DID-ZVM-X.
Bill.
DID it again. This is really the only brand I've ever considered for such a vital bike part.
Paying less could cost you dear.