Thank you! I appreciate it. We also have a 2004 4runner with about 160k miles on it and i have been using the synthetic oil and changing it every 10k. I also put the mobile 1 extended filter.The extended interval oil retains is viscosity and other properties for 15K miles, but that doesn't mean it will be clean enough in 15K miles. The oil accumulates microscopic wear particles that that filter can't take out, and those cause wear. It's best to keep them flushed out with more frequent intervals.
Is synthetic at 5K intervals a waste? I don't think so, personally. We bought a 92 F250 truck brand new. It has a 460 cubic inch engine, a design that was notorious for being worn out at about 80K miles. We still have that truck, it has 132K miles on it now. I used synthetic every 5K, and it runs like new still. I know, because I have to do tail pipe emissions tests on it every year. It passes very easily.
I run my new motors for 10K miles to break them in, then switch to synthetic.