I just had to chime in on this one! We just had our DS4 gifted tested (he is almost 5 and is in pre-K), and your story was eerily familiar to me. We actually switched him to a Montessori preschool in January and it was the answer to our prayers.
Since there is a self-contained gifted program in our public school district, I called and spoke with the gifted ed director twice prior to having him gifted tested. She did everything she could to convince me that our local school would do plenty to support him and that the self-contained was for the "very" gifted who wouldn't do well in a typical classroom. I could not for the life of me figure out why she assumed he isn't higly gifted.
Fast forward a few weeks, we had him tested and sent her his scores. She personally called me and basically tried to talk me into the self-contained program even though it is a much longer drive for us. Point being, I was completely blown-off until I had the test scores in hand. It was money well spent!
Good luck to you!