The best thing I ever did to get my laundry clean was to install a soft water conditioner. Hard water minerals bind with dirt. So many other benefits to soft water to mention here. I know, not an inexpensive solution to your problem.
I was going to recommend Amway Prewash Spray, but the formula has changed and don't think it's as good as it used to be.
Good luck and let us know if you find something that works.