Hello i got a 2004 cts 3.6l automatic 34k miles. today i was merging onto the highway and i stepped on the gas to go faster because it was an open road and my speed stayed at 60mph but my rpms went all the way up. has this ever happened to anyone before? also the check engine light is on and has been on since we installed the automatic starter 2 weeks ago and we brought it back to the place and they said everything looked fine. what do i do.

 

Did the car quit moving? Not really sure what you mean by "speed stayed at 60mph but my rpms went all the way up." It's possible if you were going at a certain speed, that hitting "passing gear" might not have actually sped the car up.
Need to know if it was more like "neutral" when this happened, or if it stayed in gear, but just did not speed up.
It's very possible that the automatic start system could be messing with it. We also need to know what codes it has/had...that would be the place to start. If they tied into the neutral safety switch, they could have caused the PCM to think the shifter is on a lower gear range, or even Park.

 

i dont really know. it kind of flt like there was nothing resisting when pressed on the gas it kept cruising at 60 but the rpms just skyrocketed. it felt like something i would expect from the car being in neutral

 

Really, really need to know what codes it has. Several possible problems could cause your complaint....speed sensor, shift solenoid, neutral switch(MLP), funky TPS(throttle position sensor) etc etc....
Need the codes to have someplace to start.