JLady, your son sounds very perseverative. You can get this with ADHD, we get it with the combo of ADHD plus autism. It really does add to the frustration (theirs and yours). And you can't really do much about it, except teach him to find other ways around a problem (not easy - he's male, as well - triple whammy).
difficult child 3 will now move on when he's stuck on an exam question, but it's taken years to get him to do this.
I would seriously consider getting a detailed Speech Pathology assessment done on him - if he's reading well but has poor confidence, it could be language-based rather than reading-based.
In the meantime, what will help A LOT (and again, it's the opposite of how we were raised) -
1) What you're already doing - don't pressure him too hard to read especially if the book is involved or complex;
2) encourage him to use a dictionary and thesaurus, show him how and show him how it can be fun (I used to look up a word, then I would look up words given by the dictionary as the meaning, to see how closely it brought me back to the beginning word);
3) COMIC BOOKS are fabulous. They teach the language as dialogue, you get the context as well as the language itself. Plus they can be short and funny, or long and involving. You can find comic books that are deep and meaningful, targetting older teens or even adults, or you can find the really simple ones. They've been really useful for difficult child 3, even though he could read fluently as a toddler. Asterix has been wonderful (difficult child 3 even began reading some of the foreign language versions). We're now getting him to read the Discworld comic book versions. He also reads manga.
4) DVDs with subtitles - again, it shows the look of the word, he hers the sound of the word, he learns the context of the word.
5) We would read books together, one of us would do the dialogue while the other did the rest of the text (like stage directions). Or we would take a different character each. We had to read with expression, try to put on funny voices, for example. It became a fun game that was just ours to enjoy. If he's reluctant, then begin with a fairly short book and YOU read it to him, and YOU do all the characters. Make it fun and funny, ham it up. If nothing else, it should give him confidence to one day make a fool of himself too, without feeling embarrassed.
I hope the risperdal works OK for him. Watch for sleepiness and weight gain. It mightn't be a problem; or it might. We found that the added weight came off again, when the child stopped the risperdal.
Something else that can work - breathing exercises, including learning to breathe from the diaphragm and taking 6 seconds to breathe out and six seconds to breathe in.
There are a lot of things you can do, at home and free from expensive therapy. That's not to devalue therapy, just that some things you can begin on your own.
have confidence in your skills as a parent, as well as your desire to be on the stage - use it to brighten your lives with some hamming up, and have fun! It's also darn good therapy!
Marg