Wyldkat, have you considered OCD (obsessive-compulsive disorder)?
My gifted dd (now 13) had extreme sensory issues and hours of tantrums every day as a toddler. Everyone told me she would grow out of these terrible 2s, but her 3s were even worse and by her 4th birthday we knew we had to get professional help.
She could not handle transitions at all. Any change to her normal schedule could set her off. She was great out in public and everyone thought she was a little angel, but she would pen it all up inside and let it loose once she was home. These tantrums could last for hours and were becoming violent. In addition to tantrums, she couldn't handle socks, underwear, tags, new foods, bright lights, loud sounds, etc.
We audiotaped some tantrums and kept a log book for about a month documenting what triggered the tantrum and how long it lasted. Then we visited a child psychiatrist. She was diganosed with atypical OCD and put on a very small dose of anti-anxiety medication. The medication began kicking in after a couple weeks and the tantrums slowly became less and less intense. After about 3-4 months of medication, she no longer had any sensory issues and her tantrums ended completely. The medication was a life saver!!
Now she's 13 and still on the same medication (an adult dose now to go with her adult-sized body). We always know when it's time to increase her medication (as her body has grown larger) because the tantrums, sensory issues, and inability to cope with change/transitions appear again. I have no idea how we would have survived the last 10 years without her medication.
It's very atypical OCD. She has no germ hang-ups or weird rituals. Her only compulsion she has is that life must be absolutely perfect and predictable. But, that compulsion goes away as long as she swallows a small pill every night.
