My 2002 Tahoe started a new habit yesterday morning. It started up fine, let it idle for a few minutes before driving off. I drove about a mile to the end of my street and came to a stop sign. As I proceeded from the stop sign and got back up to a speed of about 35 MPH, I noticed a persistent surging in the engine. While holding the gas pedal steady, I could see the tack changing by about 500 RPM causing a corresponding change in vehicle speed. If I try to accelerate, if seems to run and accelerate fine, but the surging shows up again while at a steady speed. Once fully up to temperature, I cannot detect any surging.I have not scanned for any codes but there are no check engine lights on the dash lit up. Ideas anyone?