[QuietMike]

I have a 2003, but the manual for 2004, it shows to measure the chain slack on the bottom chain, but all the videos i see show only people measuring the top chain, i assume the manual is correct even for my year, but i wanted to confirm with somebody.
it says 20-30mm in vertical play on the bottom chain

[Back2-2]

That is correct. The lower chain length is under no tension when at rest. Elevated rear wheel and recheck after torquing the rear axle nut.