very unlikely that bad old oil is slowing the bike. if oil was so bad, bike would be overheating and sounds would be different.
the problem COULD be in the engine, but as it's a lot of work to take it out, disassemble and check, best to eliminate systematically all other simpler causes.
For example, a new chain on bad sprockets will not solve a noise problem - send a picture of your sprockets, front and rear.
Same for the rollers, take them out and examine, send picture
you say you have tensioned the chain by the manual, still take a picture of the bike so we can see how it looks.
if you are asking for help, help us to help you by posting these pictures
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