Sonata NF (2006-10) :: Overheating / Idles Really High Only In Gear And Vacuum Boost Gone

I have a buddy with a 2006 Sonata, 3.3. It has about 138,000 miles on it.

When it gets hot, it will LEAP into gear. As if when you put it in gear, the throttle is pushed open 10% or something. Kinda like you would do with an old Ford or Chevy (like the 70's) that stalls when you put in gear. When it gets really hot, like after driving it for 30 or 40 miles, when you come to a stop, you lose the vacuum boost on the brakes, and the engine just goes on the pre-detonating rampage! It literally sounds like Dodge with Cummins diesel in it! It's fighting you while you struggle to keep it from LAUNCHING off the line. The strange thing is, as it is put back into N or P, it returns to normal instantaneously as if nothing was wrong in the first place.

My bud took it to the dealer, here is what they think it could be:

1. Clogged cats (nope, no back pressure, already checked)
2. Wrong spark plugs (it does not have the OEM direct replacement, it has some kind of dual electrode deal in it, but the part number crosses as an acceptable replacement)
3. The dealer did say that the ecm is up to date and that the throttle body is calibrated. That's what I thought it was in the first place.

In my professional opinion, I think it might be a ragged out timing belt. But I'm a domestic mechanic, not so strong with the imports (not trolling here, seriously, I work with fleets 99% of the time).

And there are no codes either.