Welcome to DF. You'll find that this is a great site with some very knowledgable members.
Since the 5.9L has a true distributor system it doesn't have an actual camshaft position sensor. It actually uses an "Ignition Pickup" located on the distributor (someone will correct me if I'm interpreting this wrong). That's why the guy at the parts store couldn't find it. I'm certain they carry it, Auto Zone does. Nonetheless, this is directly from the service manual:
The camshaft position sensor is located in the distributor
on all 5.2/5.9L V-8 engines (Fig. 6).
Distributor removal is not necessary to removefrom the distributor housing.
camshaft position sensor.
(1) Remove air cleaner assembly.
(2) Disconnect negative cable from battery.
(3) Remove distributor cap from distributor (two
(4) Disconnect camshaft position sensor wiring
harness from main engine wiring harness.
(5) Remove distributor rotor from distributor shaft.
(6) Lift the camshaft position sensor assembly
I would probably replace both sensors if you can afford to. If not, start with the crankcase position sensor. They are about the same price (~$45 each).
Also, the average battery life for Durangos is about 4 years. If your battery is older than that, it may give you problems like a rough idle and stalling at low RPMs, even though it may have enough juice to start the truck. Regarding the corrosion, you should definitely clean the posts and cables. However, it doesn't necessarily mean your battery is bad.
When was the last time you had a thorough tune up? If it's been a while, you should change out the spark plugs (champion copper gapped at 0.040), cap and rotor (brass contacts), and clean the throttle body. There are tons of posts on here about preferences and techniques. Check out the FAQ section for help with these items. There is a lot of great info there.
There are several very active members on this forum, so you should get more advice soon.