Calvinist doctrines most definitely are not Augustinian nor Pauline and, as the Swedish Uppsala synod of 1572 called it unbiblical and banned it from Sweden, leaving only Lutheranism, well..
Augustine did not hold to the concept of “the elect caste” as did Calvin — Augustine did hold that many people who are really Christians will and have fall away. Justification, sanctification, glorification are all gratuitous and monergistic, but Augustine clearly was against justification by faith alone.
Augustine’s argument of sola gratia is not quite sola fide as per Cauvin.
Let’s also be clear that augustine did not address limited atonement.
And a big one - Augustine held to single predestination (God chooses the elect, but does not actively reprobate anyone - he simply “passes over” them), while Calvin held to double predestination (God choose the elect to salvation, and the reprobate to damnation).