Do you have any numbers to support that notion? I don't really think China depended on US to get where it is right now. It's a significant business partner, but the EU is too and actually surpasses the US. Of course, both China and Japan own large amounts of US debt, but I don't think that's related.
Just look at Chinese standards. Older, well established standards, such as mains voltage, mains frequency, PAL video format, etc., are from East Germany through USSR, which eventually became EU standard.
Then, in the early 90s during the wake of Tiananmen square incident and the West stopped to export high tech to China, China partnered with Japan. That's why many standards (discrete transistors, material science, textiles, etc.) developed in that era were similar or identical to Japanese ones.
In the new century, as China joins WTO and buys US debt like crazy, many US technology got imported to China again, including networking, computing and similar digital stuff, and thus many new Chinese standards are similar to US standards.
So while Chinese technologies are not 100% based on US ones, but many later ones after the honeymoon period between China and Japan has ended, are.
As for why China and Japan can't get along well forever, well, it's a nation level hatred.
Chinese people can get along with Japanese people and Korean people, and vise versa. But Chinese government always have this hatred to Japanese government on Japan invasion, so does Korean government. It's a political stunt to gain public support.
Economically, China, Japan and Korea form a very strong alliance, but politically we just can't get along. China can get along with South Korea, but neither can get along with Japan politically.