I agree with the other comment - it would be helpful to get the autism possibility figured out. There are definitely specific types of behavior modification that work better or worse and acting out behaviors can certainly be part of the condition.
You mentioned quite a bit of climbing as the primary behaviors that you are having difficulties with. I have noticed with my little ones that they collect a lot of energy in the cooler months and need an outlet. Last fall we got a climber that we put in the playroom for them to have a way to burn up some of that energy when we couldn't get outside. I actually found it through the Pennysaver, but it was in great shape so with a quick scrub it was acceptable for inside use. It's not a huge one - just a cube with 2 climbing walls, a small door, small slide, and tunnel holes. We found that we regained a good part of our sanity when we gave them a safe and acceptable outlet for their energy. Now mine were not climbing fireplaces and entertainment centers - not that advanced in climbing. If this doesn't sound like something you have space for or would work for you, I would still strongly recommend making some kind of big muscle activity a priority in your daily planning. Whether it be a park, the backyard, a gymnastics class, or the play area at the mall, it sounds like your little guy needs to climb so you need to help him find appropriate times to do so regularly. Giving mine a place to climb stopped them from climbing on other things that were not ment for climbing.
You also mentioned finding a preschool to take on your child's special needs. You should contact your local school district. The school districts or counties are responsible for providing services for children with special needs from birth. Usually it is done in the home from birth through 3 and in a preschool setting from 3-Kindergarten. OT, PT, and speech should all be available in the preschool setting if your son needs any of those services. You said your son didn't talk until 2.5. I would imagine that it's possible he is still a bit behind in language. This could qualify him for services. Sometimes your pediatrician has to give a referral or complete forms for the programs so be sure to talk to them about your concerns and your local programs. Chances are that they have other patients that we involved in some kind of early intervention program either currently or in the past. I am a stay at home mom now, but was a kindergarten teacher and psychology/social work (did my practicum in an early intervention program but not locally so I do not know the specifics for this or your area) graduate in my past life so I do have a bit of background in the area.
Good luck - it's not always easy working through the system to get the resources that your child needs. Remember that you are his advocate and he needs you to help him get what he needs. Trust your instincts and reach out to the professionals for as much help as you can.