I think Justin Amash is a Trump hater, period. He used those reasons as a convenient cover for his hate.
I don't disagree that Amash has detested Trump all along, and I can't begin to guess what his entire motivation is. But Amash was also a fierce opponent of deficits and government spending. And in that he has always been at odds with just about the entire Republican party in Washington. For Sanford to claim the GOP was the party opposed to "debt, deficit and government spending" ignores their history. Sanford's hatred of Trump is also personal and has nothing to do with fiscal positions.