@thefallen21
I thought I would share my experience working on a SIM integration. If you are using silent post urls and relay responses, it is possible that the new sha512 validation is slowing you down somewhat if you have implemented it.
This particular client had a not well known commercial CMS that had unfortunately been botched by the previous several developers who had worked on it. I noticed once we implemented sha512 that the relay back slowed down considerably. Had it been less database intensive and in particular if the application hadn't been botched the sha512 wouldn't have had any noticable effect. It was just that the backend was designed so that every single thing that had to be done took a long time. So when you switch from 5 parameters to 30 it slows it down that much more.
In your case however, 5 minutes is extreme. I would bet very, very high that your issue has nothing whatsoever to do with authorize.net. You are using either a button to redirect back to the page or you are using a relay reponse that does it automatically. That is what I presume. In either case, what usually happens is there is backend code that does actions on the order just placed. Did you edit your code, or did your developer around this same time? It sounds like you have some nested loops or loops that take a long time to resolve.
I have been working with authorize for almost 2 years now doing integrations. I have used a lot of different methods, including straight calls to the API with no hosted form, Accept Hosted, and now SIM. Authorize.net responds very fast on all counts. With webhooks, they're on your endpoint in literally 3 seconds. With SIM, as soon as the transaction completes they are redirecting to your relay url, instantly. So whatever is slowning you down has to do with your application. It is almost certainly the backend order processing that takes place after the customer completes payment. This assumes that as you stated above you have eliminated the IP address issue as a possible cause. The timing of the IP address change and your issue seems like a big coincidence, and I would be double triple checking there too.
A good test to run would be to set your redirect or relay url to a page on your site that is not conneced to a db and runs no programming whatsoever. I would just make up a plain html page that says hello world. At the same time make your silent post url a plain html page. Does this briefly for testing purposes. Run a test transaction and see if you are instantaneously taken back to your site. If so, you have eliminated any delay on the part of authorize or your firewall.
