Reduced Engine Power (2003 Suburban)

This morning when I started our 2003 suburban, I put it in drive and then received a message on the LCD display that said "Reduced Engine Power." The engine continued to run, but when I pushed the gas pedal,
nothing happened. No revving, no acceleration, nothing.
I'm not sure if this is applicable or not, but we've been having some electrical problems when starting the vehicle. If one of our children leaves the door open for a while and we try to start it, it struggles a little bit at first but will usually start. This morning, this electrical problem occurred again, but it started up okay. And then I received the message above. We've had a GM dealer look at the alternator and battery and everything is okay (according to their tests).
If anyone has any thoughts or ideas about this problem, I'd love to hear from you! Thanks in advance.
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I had the same problem this month(2003yukon) it happens 3 times to me i went to the dealer and they said : this problem because I modified the lights from halogen to xenon they told me you have to remove the xenon kit because it takes too much electricity from the car. so if u made any electrical modification u have to remove it.
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