Yes you will need to downgrade to CP13 first, look at post #1 in this chain for which files need to be unlocked. Once you have all the files and run the update you can them flash CP17 again
So I can go directly from CP13 back to CP17 in one upgrade or do I have to do them in order CP12 then CP13 etc?
Also what do I do about the two missing files I can't find. Apparently my NUVI 265W was never equipped with the 3D/DEM capability so that's why I can't find the GMAPDEM.IMG fille as well I am not sure about the D3406300A.SID (02/27/2020) file and why it isn't in the 2021.10 files I have.