the over revving problem sounds odd to me, but all i can think of is the it has something to do with the transmission. also, you said that the engine revs at 1500rpm when its first turned on in the morning. my aurion does do that when i turn it on when its cold, and the revving reduces about 1/2 min afterwards. a toyota mechanic said it was designed that way to help the oil and fuel to flow through all components of the engine. this is for the new models with 3.5 ltr v6's such as aurions, klugers, v6 rav4s ect... your hilux has a 4 ltr v6 i think, and i don't know if its similar or not. after all, i suggest you should bring it in to a toyota dealer to let have a look at it.