2006 Trailblazer Dummy Lights

[TJsDAZE]

I have a 2006 Trailblazer 2wd 4.2 6 cyl. the chck engine light came on so I took to adv auto they gave me a code p0449 for vent valve solenoid. i found a diagram on this sight for location and had dealer replace it and new battery. Now the ABS, Stablitrak service light and Stablitrak indicator light is going on and off intermitantly at the same time, sometimes on and off sometimes stays on, this starts after veh has been on a while. when first came on was on highway felt like veh was shifting gears. hasn't done this since then. I took it to dealer said it was coding rear speed sensor but when the sensor itself was checked it was good they checked all wiring and leads connections ? Dealer said wait for lights to come on and stay on so they can get a better read. Is this good advice or are we overlooking the obvious or just misdiagnosing the problem. I am confused Please help any help is good help. PS I am a newbie this is my first posting (book lol) I hope I am in the right forum.