I find when reading boxed text, it's vitally important to:
-Read it in a slightly rushed monotone, quite different from your normal GMs voice.
-Accidentally skip words, or even whole lines
-Go back over what you've just said, and then read it all out again
-Skip forward from the box and read out parts of the room description, including things the players shouldn't know.
-Not let the Players interrupt you while you're reading it out, and starting back from the beginning if they do.
-If there's a scripted part between two NPCs get their names (or voices) mixed up so no-one has any idea who has said what.
Sadly I've been in games, and run games where all of these have happened. I don't mind Boxed Text, but as GM of a certain age it does often come with a certain amount of baggage applied.