Never had any problems getting that mileage out of a chain on the Dakar (heavily laden). For tension I usually try and see if I can get it to touch the swing arm when I sit on it by lifting it with my boot. If it doesn't touch it's about right. After doing it the way from the manual you tend to know how much slack is about right. Tight is worse than a bit on the loose side.

Lubing is simple. I do this every night after a ride. Wipe the excess grime with a cloth. This is only if there is any, which there usually isn't with this method.

Then I drip ATF over the whole thing by spinning the wheel, or just stationary (I don't tend to ride with a chain guard if I can help it) and brush it in with an old tooth brush. It'll drip off and soak in overnight and keep the thing nice and lubed.

ATF isn't sticky, so it's never a grimy mess. Not even in mud because everything just falls off and lubes the o-rings perfectly.

Chains last ages. 2 bikes with fresh chains through South America for just under 20k km and I sold them a few thousand k's later at home with the same chain. I actually find the front sprocket tends to wear first. I went for Chaingang (Australian company) hardened rear sprocket. But the front was a typical one. Heavy duty chain though.

Never had drive chain problems ever.

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