The differences in scores can be attributed to different scoring models. Credit Karma uses the VantageScore, which is a completely different model from the traditional FICO. So your Experian VantageScore naturally wouldn't be the same as your Experian FICO 8. However, you'll note that I said "FICO 8." That's because FICO also has several different scoring models that they use. FICO 8 is the most common model today used by credit card lenders. However, car loans and mortgages use a different FICO score, and FICO recently released a new model called FICO 9, which obviously also has different scores.
Each scoring model weights things slightly differently, so your Experian score will almost certainly vary somewhat from model to model. That's completely normal.
I believe Amex does give an Experian FICO 8, but as I said Credit Karma gives a VantageScore (whole different model, unrelated to FICO). I have no idea what USAA gives, but it may be a different FICO score. Bottom line: you (and everyone) have quite a few different Experian scores and they'll vary depending on the model. Before applying for something you'll need to determine what scoring model and bureau your lender will be using to evaluate your credit.
Regardless, congrats on the great scores!