So I was talking to a friend of mine who is a machinist yesterday. He told that recently he had seen two sets of heads from 3.4 L Toyotas with burned exhaust valves. He assumed it was because people were not getting them adjusted on time.
Today I called a couple of dealerships to see what the service schedule is, and how much they would charge to do the work. My truck has 72K on it. I almost never have work done at a dealership, but I thought I would ask anyway. I was asked if they were making noise. I said no, but if the valves were tight they wouldn't make noise anyway, and that's when you have burned valves, not when they are loose. The mechanic said that the valves will get loose, not tight as the shims wear. So if it isn't making noise, don't worry about it.
I don't really know how shim and bucket valves work. Is that true? do the valves on this engine get looser or tighter as the shim wears? If it is true, I won't worry about getting them adjusted. If it isn't true, I just found a place NOT to take my truck.