Fonts and images for PDF letters not printing correctly

Edit: Just realized this may actually be a problem with our recent installation of wkhtmltopdf.

Set up Print Page (PDF) Formats with margins and fonts the way you want them. Name the format (e.g. Plain) and make it default. To create a PDF template in Message Templates, choose the page format you just created and create your letter template.

The problem is that when you go to create a PDF letter for a contact, the Plain format is not automatically selected. The template "Default" is selected with no margins set up. You get an error and have to manually select your "Plain" format. Then when you push the Make PDF button, your PDF gets created, but the text is all in a sans-serif font, even though I set up the template to use a serif font (Georgia).

This also seems to be resizing my header image weirdly. I had it set up in the previous version of Civi (6.1.2 or something) to span the page from margin to margin. It is now much too small. I've attached a "before" and "after" example.