These two codes indicate an evaporative system leak has been detected by the Leak Monitor. The code P0442 indicates a medium leak and P0455 shows that it escalated to a large leak.
First, some background on the system. Your fuel system basically consists of two parts: The liquid and the vapor portions.
Liquid, you know about. Fuel doesn't stay liquid, though, in your fuel tank. Gasoline would evaporate away if given the opportunity. The job of the evaporative system is to manage these vapors. They're held in the tank until internal pressures push them into a storage device called the vapor canister. From there, they're piped to the engine compartment and become part of the purge system. The purge solenoid opens under control of the PCM to allow metered amounts of vapor into the engine to be burned as you drive.
Your evaporative system includes all vapor lines and controls REARWARD of the purge solenoid. The codes you set indicate the problem lies somewhere between the gas cap and the purge solenoid, so this is where you will need to direct your attention.
First, check your gas cap. Very lightly, use the spring tension on the cap ratchet mechanism to turn the cap a little to the left (loosen). If the cap is loose, it will fall off easily. Tighten it at that point and you're done.
If it wasn't loose, it could still be defective. Caps develop evaporative leaks all the time. Unfortunately, there really isn't a good way to test one at your end. Replacement is easier.
The next check would be underhood. Your purge solenoid and lines are located on the right side fenderwell area underhood. It's very near the leak detection pump (LDP), which is what originally determined your leak problem.
Check for cracked or detatched hoses at the purge solenoid and LDP, following the hose harness as far as you can see. It will lead you to the next stop, if needed.
The vapor canister is located on the right side outer frame rail on your 2001 Ram. It's a two-piece unit, with a round and a square-ish canister mounted on a metal carrier. The hoses come into the canisters from the top, making inspection difficult without removing the carrier.
The carrier is held in place by four bolts (13mm hex head). Two at one end, one at another and the fourth in the upper center. You will need a 6" socket extension to get that one.
Once lowered, check all rubber in the area. The large hose goes to the LDP. The small (1/4" dia) hose heads toward the tank. And there is a pass-through (U-shaped) hose that connects the two individual canisters. This is the usual area where the leak is found. The canisters are sometimes damaged by contact with road debris, so look for signs of plastic trauma.
The pass-through hose is available separately. The small 1/4" hose can be cut from bulk. But the large hose connected to the LDP is serviced with a new hose harness only. You will need to see your friendly neighborhood Dodge dealer for that part.
The last possibilies for setting these codes are leaks above the fuel tank (sometimes given away by liquid fuel staining down the sides) or a failed LDP (rare).
Once you're confident you've found and repaired your leak, you can do two things to remedy the MIL light being on.
Nothing. The system will test itself each morning within minutes of start. Once two Good Trips are logged, the PCM will understand that the problem is no longer present and turn the light out.
Do a battery disconnect. This clears all information, including adaptives and such. It works, but the engine may run just a little different while the PCM relearns.
Either way, you should know within a few days whether the repair was good or not.