My 2001 Silverado has what I believe is an idle issue. The idle will go up to 750 RPM's and then drop to 250 RPM's. The other day when I drove it I had to put it in neutral when I was slowing down and press the gas pedal to keep the truck from stalling. The fuel pump and filter is only 4 months old. Any clue what the problem might be?

Thanks.