Mark, sounds like you need to either replace your solenoid block and/or your valve body.
Yes, these can be done yourself. Both could be done over a weekend, or even a day if you are mechanically confident.
Try doing some searches, here in the tranny forums, and see what you can find. I know there's a lot of threads on this topic. If you still can't find anything, let me know and I will see what I can dig up for ya.
