The reason diesels get good results is because it alters boost levels along with fueling and timing maps. There is some power to be pulled from the factory maps based on the fact that they are safe maps. Programmers will be able to tune maps for optimal results, which isn't always a universal thing. Running a "chip" is like throwing on someone elses tune and running it blindly.
Urd has made a map with the MAF cal and pulled 15-20hp from a stock Tacoma.