1. The dirty throttle body is caused by the re-circulated exhaust gas and is expected in a car equiped with EGR system. Usually it is fine, even it looks dirty.
2. If a car has the transmission fluid cooling circuit to cool down the transmission fluid, usually it is fine not to replace the fluid unless you really drive aggressively. But I drain the fluid every 30K miles anyway. I do not flush the system.
There are two different ways to flush the transmission. First is flush through the regular flow direction, which can be a DIY. But I don't think it is very different than the Drain and Fill. If you want, you can do several Drain and Fill in a short period of time to achieve the same result. The second is reverse flush. The new fluid is pushed through the system in a reversed direction. By this way, all the particles on the transmission filter will be pushed back to drain pan and drain out off the car. So you have a clean filter and the fresh fluid. However, some car manufacturers do not recommend the reverse flush. If you want a flush, make sure what type of procedure is used and that those people really know what they are doing to your car.
