This was a HUGE jump for you. Adult m/s to peds m/s to eventually PICU, or Adult ICU to PICU *would* have been easier, however, you sound like an excellent conscientious nurse. So give yourself some credit, because you deserve it.
Pretend you are brand-new again nurse again (because you basically, are), and don't set too high of expectations for yourself to learn or learn to critically think faster than you are humanly able. In your off-time read up on what you have experienced on your orientations days.
If your preceptor is rude, ask that he/she treat you with respect. Explain that you are struggling, and his/her workplace incivility (WPI) is making it more difficult. Feel free to throw out there that WPI negatively affects morale, and negatively affects patient safety - because it does. This person has probably never been called on their BS before. You are an adult, so act like one, and speak up for yourself. If this fails, and your preceptor is still a jerk, ask your director for a new preceptor, and outline why.
And to repeat, give yourself some credit!