IPhone 5 and Syncing Issues?

I recently bought a new phone and laptop and want to sync my phone with the new laptop, so I don't have to always revert to my old laptop when I want to put music on my phone and everything. In order to click the box that says "manually manage music and videos" iTunes wants me to remove all music from my phone to sync it with the current iTunes library. I have no problem with that, except for the fact that each time I've tried to do that, it doesn't finish the job correctly and ends up leaving either tons of duplicates of each song on my phone and neglects to put certain songs on there, or it doesn't sync anything at all and instead screws up the music on my phone to the point where it won't play anything for me. It's extremely confusing and I'm likely doing a poor job of explaining what's happening, but in the end I always have to restore my phone because it'd take too long to remove each song individually.
Basically, I was wondering if there was an easier way to sync my new phone to my new computer. I'd really like to put this case to rest so I can stop having to deal with it. Perhaps I'm over-thinking it, but I can't for the life of my figure it out or find good advice online. Any help or suggestions would be extremely appreciated!
Again, sorry if I made it more confusing.

This happens from time to time with lots of stuff being synced. Try setting the music to manually sync. Restore your phone removing everything to make sure nothing is already wrong. Then go to the music sync tab and sync it. I wouldn't try syncing it all at once if it is a lot. Just sync chunks of it at a time adding more and more each time. It might leave some songs out on the first few tries but after syncing it 5 or 6 times you should get everything you want on it. Keep in mind this is for if you have 30 or 40 or more gigs of music on your phone.