I have a 03 Z-71 Chevy with 75000 miles on it. It has recently started to idle real strange when I first start it up. It sort of just goes up and down kind of like I'm pressing the accelerator just slightly and letting off over and over. Once it warms up a little it stops. It's usually doing it until I get to a stop sign about 1/2 mile down the road. When I get to that sign and stop it's idling normal. I put a brand new battery in it yesterday if this might have something to do with it. It wouldn't start so I just replaced it rather than attempting a recharge. Any suggestions?