I can relate to everything that you mention in the above post.

The 300SD will run away from the 300SDL at speeds below 30 mph. The SDL just feels very heavy and slow until the turbo kicks in. This is largely because the vehicle is running without sufficient fuel at low speeds. For those who have adjusted the ALDA on these, the performance improves significantly at low speeds. I haven't done it yet, mainly because I don't drive it around town enough to worry about it.

The power is there. You just need to press down those size 12's to get it.

As far as the cracked head is concerned, there really is no data to show that the trap will contribute to it. The theory is that the head may crack at some point if the engine was ever overheated. And, on the 603, this happens very fast if the belt is lost or coolant is lost. Most owners of these vehicles will have what is considered an overheat condition if any cooling system failure occurs. You have about 1 minute to get it shut off.