It's rockygirl, writing under my temporary name, peevedrocky.
Anyway, I used to have this problem. It took a while, but I did this.
When I got home from work I made a short to do list. I put on everything I needed to do from wash dinner dishes to walk dog to correct papers. I crossed off the things one by one and didn't go to sleep until they were all done. The feeling of "doneness" helped me sleep. Eventually, I put less and less on the list, and I don't need to use it any more. I never have racing thoughts now.
For me, it wasn't the ability to relax, it was the stress of not having things done. I would get up in the middle of the night to pack my lunch for example. Now, if I don't get my lunch packed before bed, I just know I'll go out the next day or something. Much less stress.