well in my case, to be sure it would work, first I would upgrade the kernel and system kext while in 10.5.2...
After I was sure the system was stable and running smoothly, I upgraded to "AMD 10.5.3" which, yes, is 10.5.3 but it is also what you want to look for when searching the bay. After that's installed and the system runs smoothly, I would use ASU to upgrade to 10.5.4... This method has worked for me a bunch of times (as I frequently test out new ways of installing to test partitions). Now I simply save the Mod-updates as they come out so I will not have to make a huge combo-update-jump in the future. Hope this helps.

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