Cam shaft position sensor question

My 2001 Dakota 4.7 recently displayed and engine code P0340 for the Cam Position Sensor. Even though my truck has been starting and running beautifully, and showing zero signs of a bad sensor I went ahead and replaced it and immediately the check engine light went away and all seemed to be well. After driving for about a week the check engine light suddenly appeared again and when I pulled up the code I found it was the same P0340 code again.
Since the truck was starting and operating perfectly, I decided to ignore the code just to see what happens and after driving with the check engine light on for a few days, low and behold, the check engine light went out again. Now, I've been driving again for over a week and still the check engine light has not re-appeared.
I'm beginning to wonder....if I actually fixed anything by replacing the sensor.
Somebody told me if I replaced the sensor with just an aftermarket, rather than a Mopar part, chances are the check engine light will return again. He said for some reason Dodge products don't like aftermarket parts in some cases.
I was also told, that the Crankshaft Position sensor could be going bad, but I would think if the crank sensor was going bad then wouldn't I be receiving a separate code for a bad crank sensor?
I'm wondering if the experts on this site think any of this is true.
One other thing.....when I replaced the camshaft sensor, I did not clear the engine code. When I started the engine after replacing the part I noticed the check engine light went off all by itself without me clearing the code. Could it be that I keep getting the same check engine code because I did not clear it after replacing the part?