Is there a difference between exhaust cam and intake cam 2003 cts

One crank sensor. It needs to go on a scanner. Both sensors are probably OK. Your problem is most likely the timing chains or guides. If ti were the crank sensor, it wouldn't start. Cam sensor would throw a cam code. Correlation means the crank and cam are not in sync. If you have VVT, it could be the actuator.

Too big a job for an answer here. Best to buy a service manual if you want to try to do the job yourself

With Cam Caps loosened, FIRST loosen timing chain tensioner, press it in to loosen tension, Crank using ratchet to TDC (Top Dead Center on crank pully, (to keep from damage to pistons), align Exhaust Cam Timing Mark to mark on #1 Exhaust cam cover, then take up slack between Exhaust & Intake Cams (on top between the cams), Then align the Intake Cam to mark on #1 Cam Cap, "Now" loosen the 17mm bolt to tighten timing chain, rotate engine using rachet two times, reset TDC at the crank, and look at "Cam Timing Marks on both the Exhaust, and Intake Cams. If you did all this correctly the "Timing Marks" should be lined up so TDC,Exhaust, and Intake marks are all the same.

I don't know if you have the capability to zoom in on the picture I attached, But the cams are marked with R EX for right exhaust, R IN for right intake and L EX for left exhaust and L IN for left intake. The circles on the picture are showing where the marks will be on the cams. I hop this info helps!

Check fuel pressure, and exhaust back pressure, Exhaust backpressure high would indicate restricted flow... probably restricted converter.

WOT MAF should read over 800 gs. with boost around 15psi.

If exhaust is clear and intake not plugged up with carbon...very common.... clogged injectors.

2.0 PD is self timing as long as the belt marks line up.

Also cam lobes for injectors wear out.

Still no power ? Replace injector tips/nozzles.

Did you ever find a solution to this? I am having the same issue on 2,4,6. I have replaced the coils. checked the intake for vacuum leaks. I am lost here let me know if you find anything and I will do the same.

sounds like the initial timing is way off. is the firing order correct?

cam position sensor installed correctly?

I cant find a pic of the loctation.

It is under the intake in the back in the coolant bridge it is not bad to change if you are not affaid to take the intakes off but to get to it you have to take the intake off

Yes - on the V6, the left intake cam and exhaust cam are on the same side of the vehicle. Facing the engine, the "upper" cam sprocket on that side is the intake cam, and the one that is lower and farther out toward the fender of the vehicle is the exhaust cam.