Service Engine Light On problems of the 2003 GMC Yukon

The service engine light and traction control turn on and the information center on my cluster reads "engine power reduced" and "stability system disable", then my speed is reduced and only runs between ten and twenty miles per hour. I have to turn off my truck and turn it back on after a few minutes to continue, but this problem has happened on a daily basis. I think GMC is responsible for this and more similar problems.

Since November 2008, my 2003 GMC Yukon xl 2500 has had episodes where the service engine light comes on and the engine goes into reduced power mode. In this reduced power mode, the vehicle will reach a top speed of around 25mph. I have taken it to numerous gm dealers to fix the problem, and they have replaced the throttle body assemble and wiring harness multiple times and the problem keeps recurring. I have bought a scanner which I can erase the codes because it is very dangerous to be driving 65mph with semitrucks on your tail when you suddenly for no reason lose power and can't get over to the side of the road. There have been many close episodes where we were almost in an accident. After the throttle body was replaced in Dec 08, the reduced engine power didn't come back until April 2009. Dealer then rewired the harness and it stopped until the fall of 2009. Since fall 2009, the service engine light and reduced power mode come on sporadically. In February 2010, the problem reappeared, but now the truck stalls when the engine light comes on and reduced engine power is enabled. This is very dangerous, as during the stall, all power steering and braking is lost. I have been driving down the road, turning, crossing traffic, and the light comes on and the truck stalls. This is very dangerous and scary. The truck has been in the gm dealership service dept for the last 3 weeks. Everytime they say it has to be the throttle body, they replace it, I bring it home and a couple days later we are back to reduced engine power with service engine lights. Trouble codes are p2135, p0120, p1515, and p0220. I have spent nearly $2000 on service that has not resolved this problem and they don't know how to fix it. I have read online many others have the same problem. This truck is dangerous to drive now that it stalls every time it goes into reduced engine power mode (which happens multiple times on every time I drive it).