@LeadoutMedia – That’s awesome. I’m happy to hear that it worked for you.
@UDS – First, full disclosure; I’m just a noob. The Swift guys knows a hell of a lot more than I do so definitely defer to them over any of my suggestions…
That seems odd that it had no effect whatsoever. My first thought is that maybe the WP Visual editor is the culprit. But I don’t think that’s logical because you would still see some sort of response from the custom css. In any case, here’s some things that may be worth checking/trying…
If you’re using the Visual editor, try switching over to the Text tab and enter your text directly in there. In my experience, using the Visual editor, as well as simply switching back and forth between the Visual/Text editor, often results in code/structure changes and/or   and <p> tags being thrown in all over the place – both of which either throw off the layout of your content, or completely break it so that it doesn’t display at all. So maybe try that out.
<h1 style="text-align: center;">KEY METRICS: A Look At Your F&I Performance</h1>
Ensure that your extra class is entered without the period. ptb2 -not- .ptb2
If you have more than one extra class, separate each with a single space – no commas.
Check your line height in the font size options. If it’s set much higher than the font size, try adjusting it down. My h1 is set at font size: 60px line height: 72px (just for reference). Also don’t think this seems very logical, but wouldn’t hurt to check.
Check your custom css for anything that could potentially be overriding the ptb2 code block. Good place to start might be by checking anything that you have declared !important.
Try disabling your plugins one-by-one, refreshing the page each time to check for a change in layout. Highly unlikely/probably impossible for a plugin to be the cause, as I would think you would be having issues with more than just that one element.
Well, I’m fresh out of ideas. I hope you’re able to get it figured out! Hopefully some/any of this is helpful.