Gratitude is a broad term that manifests itself in many different forms and has many different intensities. It is not necessarily performance of some rituals all the time, but rather a set of traits, which if employed are a manifestation of Gratitude itself.
Islam starts from ‘ibadah‘ which is infact submissiveness of a person to Allah. This submissiveness then extends to rituals of worship, matters of ethics and morality and other matters for which Sharia is given (See: Discussion 32787). Following all these directives is in infact show of gratitude in some way to Allah. Pinnacle of Morality is what Quran talks about which every Muslim should strive to achieve and this is something, if achieved, can also be called pinnacle of gratitude.
For Details on Pinnacle of Morality, please see:
Discussion 37174