Knocking sounds coming from either the camshaft or timing belt area the the check engine light is on and throwing a code for a miss fire on cylinder 6 does anyone have any ideas?

Are there any driveability issues? Does the vehicle drive ok? That po300 code can be a pain. Just about anything can cause a miss-fire, fuel--spark--compression. Try the crankshaft variation relearn, see if it helps, you can try it w/o the scan tool? W/o that relearn, the p0300 may set. In the old days, we would do a cylinder balance test, With engine idling we would kill spark at each cylinder, one at a time, quickly, if you kill a cylinder that has no effect on the idle rpms, that cylinder is dead. Then you would check fuel--spark--compression on that cylinder. Just my opinion. good luck

po342 is camshaft sensor did you change,check any lines going to engine for cracks or broken,like air sound.

Sounds to me that you have a cylinder miss fire. Chrysler products generally set a code when a miss fire is detected. Does the shaking go away under a load (while driving) ? If the miss is always there I would focus on the ignition system and look for any vacuum leaks around the intake manifold area .

I'll bet the light is on because you have a miss-fire or two.
Have the computer scanned for trouble codes - it may tell you which cylinders to look at.

This is the direct definition of this code
Mitsubishi DTC P1390 - Timing Belt Skipped 1 Tooth or More.
Probable Causes,
-Timing belt improperly installed
-Camshaft position sensor improperly installed
-Camshaft position sensor connector improperly connected
-Crankshaft position sensor connector improperly connected
-Camshaft's relative position not relearned after one of the following have been serviced: Camshaft, Camshaft sprocket, timing belt tension-er, cylinder head, head gasket, crankshaft sprocket, crankshaft cylinder block or the PCM.

Sounds like something to do with the timing belt it self. You can go to any Autozone or Checker and ask for a code reader (they will let you use it for free) and it will show this code again. You can also reset the cars computer with the code reader to see if it comes back with the same code.

can you tell what cylinder has the miss fire?
if not take a test light and at the coil pack VERY CAREFULLY slide the test light between the PLUG WIRE AND THE BOOT this will SHORT OUT THE CYLINDERS ONE AT A TIME
now when you short out a GOOD CYLINDER it will shutter and miss fire
when you short out the CYLINDER THAT IS THE PROBLEM NOTHING WILL HAPPEN
ok now you know what cylinder is the problem remove that valve cover and check for a rocker arm that may have pulled the threads out of the cylinder head this could be the knocking you hear also check and make sure the push rod is not bent
if all the rocker arms are secure then have some one crank it over and watch and make sure you have good valvetrain movement
if you have no movement on one of the rocker arms then you have a camshaft problem
hope this helps good luck
and if you have anymore questions let me know

sounds like the water pump bearing is worn out and has detroyed the water pump shaft seal.
coolant is leaking thru the seal area ,due to the bearing worn out --hence throwing the water pump pulley out of alignment.
The water pump pulley runs of the timing belt.---hence the knocking --either from the pulley or belt chaffing against the timing cover or even throwing the engine timing a few degrees off.
Need to replace water pump and timeing belt and anything else that may be damaged.
That's why, when ever you do a timing belt always do the water pump too.

Sound like your timing belt jump a tooth, and now your getting a camsensor code, also one cylinder has 50% less compression then the others not good, also if engine is knocking you will be needing an engine.Good Luck.

I dont think that u have a timing probing but just to be sure I would recheck the timing, (remove timing belt cover, set crank to zero and make sure both cams line up with the marks on the engine) if thats all good the u have a prob with that particular cylinder. first thing I would do is swap the coil pack from cyl 3 with another cylinder (like cyl 1) then start the car if the misfire code goes from P0303 (Cyl 3) to P0301 (Cyl 1) then u know u have a bad coil pack. try that and let me know what happens

What cylinders are throwing the codes?

What are codes being thrown, and their description?

How many miles on the SIerra?