My older son often progresses 2 steps forward and then 1 step back. Just when things are going well, we hit a bump and he backtracks. Transitions and change are still something he struggles with almost 6 years after his diagnosis.

Try to set up a routine as much as you can. Our kids really need that structure. My son does best when he knows what to expect and I give him plenty of warnings about what will happen next. If i have to change it, that's when the meltdowns happen. He also does better when he knows what is expected of him, what behaviors are acceptable. He often needs a "script" to know how to act in certain situations.

I agree with increasing his sensory diet until he gets used to the new house and any other changes. The reward system might work too.

Good luck!