The Gallo crew felt they should have been rewarded more for the Anastasia hit.

If that is true then it wasnt the first time the Gallo's got stiffed.
They whacked a Red Hook based bookmaker/loanshark on Profaci's orders who in turn promised them a piece of the deadmans rackets.
Profaci being the greedy old bastard that he was gave the Gallo's nothing.
Its no wonder the Gallo's rebelled - Profaci was treating them like mugs!