reduced engine power on 2004 Chevrolet Avalanche 1500

It started doing it when i would drive, maybe once or twice a day. Now it does it right when you start it. I cant even get out of the driveway. What do i need to change on it?

my 2006 g6 gt did the same, once or twice a day, then until i couldnt drive 2 feet. my check engine, traction control off, and reduced engine power lights were coming on. hooked it up to a computer and it read code p1125, which was APP (accelerator pedal position)
Thanks for the info, in my instance was, while driveing all 4 doors unlocked, then the ABS light came on , then there was the check brake notice. Shut the car off waited and restarted worked find for a short time then the same thing all over again with the check engine light stopped and tried again and it happened again with the reduced power notice comming on and the avalance slowed to a crawl. It's in the shop now I'm waiting to see what they found;
2 more answers
mine did this once,searched net and luckily my problem was simple by moving the gas and brake pedals up or down by control on driver door,the vehicle protects you and itself if it senses that your throttle could stick. hopefully your problem was as simple fix as mine.
The real question here is "How to I diagnose this problem?". If we could tell you what to replace without performing some tests, this service wouldn't be free.
I would start by checking the fuel pressure and also check for any diagnostic trouble codes. I would get a verification that the PCM has the latest software available as well.