When looking for a chain - look at the specs - the higher the tensile strength rating of a chain - the less it will stretch over time. Also - keep in mind - I think you replaced the rear sprocket - did you replace the front one too? If not - do so - they are cheap - and if it is old - it will wear your chain out early and make it stretch!
RIP - Yamahondaman!! You will never be forgotten!
RIP - Sam Brehm!! Gone but NEVER forgotten!
RIP - Sandpuppi101 - You will live on in my mind - I miss you friend!