The prevailing theory....and it was that....was Christ's words indicated that only the Roman Catholic church was to be Gods church, and the RC Pope Gods agent on Earth. (To me and millions of others, this is not the correct interpretation) This message was spread to RC followers was that other Christian churches were not following Gods will and direction (Orthodox, Protestant and others)....

OK, but I would state the same thing differently, and more succinctly: Other Christian churches are either schismatic or heretical. Christ gave the keys of heaven to the apostles and their successors, not to every so-called 'reformer' who decides to invent his own bastardized version of Christianity.

Do RC's actually believe in the dogma of "papal infallibility" as presented to the faithful as necessary to their salvation?

Again, stated differently: RC's believe that the Holy Spirit guides the Church inerrently in matters of doctrine, stated ex cathedra and usually after years on even decades of study by the pope and the other bishops. That has always been the Church's belief, long before Pius IX. Most of these doctrines trace their roots to the earliest centuries of Christianity, and the Church regards these traditions, along with Scripture, as divinely revealed.

So I'm not disagreeing with you so much as just looking at it from the other side of the street, so to speak.