Aside from TheGrillFather.com Maintenance Kit, believe it or not, Walmart online carries the best deep cleaning solution on the market. You should order at least 6 bottles so you can soak your grates in them, and you will be pleased. Here is the link.
Grill Tip -
What is the best way to soak and clean my caked on grates? After much research and time spent testing, we that you use these products according to the directions and soak them in a large flat closable container like a rubbermaid container and on the Third day they will come out like new.
To complete this, we also suggest you get 6 bottles to completely allow your grill grates to be submersed.
Soaking Container -