As you imply, there are plenty of places where Paul considers himself to be writing with the authority of God (Gal. 1.1, 11-12, 15-16). These verses are probably enough to settle the case about Paul's view of himself, but there are plenty more if you still think Paul didn't regard himself as having divine authority. And, as you mentioned, in Acts 22.14-15 he claims to have the authoritative commission and message from God. In 1 Corinthians 14.37, Paul says that what he is writing is the Lord's command. Colossians 1.25, 1 Thes. 4.2-8, and more.
But are there other places, or do we have other evidence that other Christians endorsed God's authority in Paul? That's a tough question, because most of the NT was written by Paul. The Gospels are the story of Jesus and don't refer to Paul or his writings, though Luke
* The other apostles and church leaders recognize this same authority and message in Paul in Galatians 2.1-10. The question at hand is whether Paul was contributing to false belief because Paul was preaching a false message. He was vindicated and endorsed by Peter, James, and John.
* In 1 Thessalonians 2.3, the people there accept his words as not human words but rather of divine origin.
* In 2 Peter 3.15-16, Peter regards Paul's writings as having God-given wisdom in his writings, and that they are on the same plane as "other Scriptures."
We can start the conversation from there. Let's talk.