Nothing they could have put in your truck is going to hurt it for a normal interval (didn't put what you do there). No need for STP, doesn't help here. Yes, probably should run the 5W30 vs. a 20 but again, I can't see any issues. You can certaily go back and request that while you understand that the 20 is back-spec'd, you'd have perfered 30. They may tell you no b/c they followed their procedures and they will most certainly say "it's fine". Your time has a value here. Next time make sure you request regardless of what their system says, you are more comfortable with a 30 grade.