I have a 2004 GMC Envoy, while I,m driving the reduce engine power light comes on then it dies! This happens 10 to 12 times a day. It will sometimes do it if I change the heat from high to low or the other way. It also uses a lot of gas when this happens. When I crank it back it takes a while before the speed picks back up.

Clean your throttle body for starters. When this is filthy, and it will be filthy, the throttle body will learn some bad habits. So the engine will go into a safe mode "reduced power". Clean the TB with TB cleaner with the battery disconnected, must be nice and shiny front and back. When finished, connect the battery back up and drive around for 20 minutes or so with all accessories off. This way the computer will re-learn a newly cleaned, properly functioning throtte body. This seams to be the main culprit with this problem. Hope this helps!