What the title says. Are there any "gotchas" or things I should be looking for or adjusting if I want to bring Trailblazer PCs into a Pathfinder module?
I can't really think of any. Which are you planning to use as your "core" system?
While both systems have their own classes, Trailblazer makes a lot more rules changes, some of which you have to hunt for in the book (for example, I cleaned up a lot of the rules and wording on grappling, including monster special abilities related to grapple). You'll have to decide which Combat Maneuver system you'll be using, turn undead, etc.
The only other thing I can think of are NPCs using Pathfinder classes, but I don't really see that as an issue. Our philosophy with Trailblazer is that it's ok for the bad guys to follow their own rules. We intended it to be drag-and-drop into whatever module you want.
It may take a little time to get used to the power level though when going from TB<>PF. I'd say PF classes and races are more powerful but TB characters get Action Points and Combat Reactions.
All that said, I'm grasping at straws to think of things and probably over-thinking it. I wouldn't hesitate to run any PF module with TB. In fact, I'm extremely intrigued by the new Kingmaker AP.
I'm definitely curious to hear how it goes though! I love the Pathfinder modules.