Valve cover replacement and Trust plate o-ring

To replace the camshaft O-ring seal. (Assuming you have a 3.5L V-6)

Easy to DIY.
Get:
O-rings from the dealer - approx $2.50 each some years ago - may be more now.
Small (1/4") ratchet drive
12, 13 or 14 mm short socket (can't remember which)
Spray brake cleaner
Tube of good RTV sealant.

Start on the passenger side - easiest to get to. Feel around the rear of the cylinder head facing the firewall. You will find an approx 2" circular recess surrounded by a football shaped flange with two bolts on either end of the football.

Use the socket to remove the bolts and a small screwdriver to pry out the plug and flange. You will see the old (flattened) o-ring. Replace it with the new one and use the brake cleaner to clean all mating surfaces. It's not in the book but I used the RTV sealant to smear a thin layer on the mating surfaces. Then insert the "plug" and replace the bolts. Passenger side done!

Driver's side is exactly the same but when you try to get your hand in there you'll find it's much harder to get to. Here are some tips.

Use vice grips or a hammer to bend the engine lifting hook out of the way towards the front of the truck.

Unbolt the clamps holding the A/C lines to the firewall so you can move them a bit.

Wrap a rag around the spring clips in the fuel lines and wrap with masking tape. This will prevent you from getting your hand shredded when you reach in to remove the bolts.

Final problem: When you finally are able to reach in and find the plug and bolts you will note that the wiring harness from the engine to the driver's side O2 sensor runs right across the cam plug and will prevent you from removing it.

I unhooked the hold down clamps and used some twine to pull the wire over towards the passenger side - thus leaving the cam seal plug free to be removed.

Once you have done this side, reattach the wire and, if you care, straighten out the lifting hook.

To replace the valve covers (i believe this covers all of the available engines for your vehcile)

Valve Covers
Removal & Installation
2.4L Engines
1. Before servicing the vehicle, refer to the Precautions section.
2. Remove or disconnect the following:
Breather hose
Positive Crankcase Ventilation (PCV) hose
Valve cover
To install:
1. Install or connect the following:
Valve cover Torque the bolts to 30 inch lbs. (3.4 Nm).
PCV hose
Breather hose
3.0L Engine
1. Before servicing the vehicle, refer to the Precautions Section.
2. Remove or disconnect the following:
CAUTION
Work must be started after 90 seconds from the time the ignition switch is turned to the LOCK position and the negative battery cable is disconnected.
Negative battery cable
Valve cover
To install:
1. Install or connect the following:
Valve cover and new gasket. Torque the bolt to 2-3 ft. Lbs. (3-4 Nm).
Negative battery cable
2. Start the engine and check for leaks and proper operation.
3.5L Engine
1. Before servicing the vehicle, refer to the Precautions Section.
2. Remove or disconnect the following:
Negative battery cable
Valve cover and the semi-circular packing.
To install:
1. Install or connect the following:
Valve cover and the semi-circular packing. Torque the bolts to 2.5 ft. Lbs. (3.5 Nm).
Negative battery cable
2. Run vehicle and check for leaks.
3.8L Engines
1. Before servicing the vehicle, refer to the Precautions section.
2. Remove or disconnect the following:
Negative battery cable
Oil filler cap
Positive Crankcase Ventilation (PCV) valve and gasket
Valve cover, gasket and oil seal(s)
To install:
1. Install or connect the following:
Valve cover oil seals and gasket
Valve cover. Torque the bolts to 27-35 inch lbs.
Positive Crankcase Ventilation (PCV) valve and gasket
Oil filler cap
Negative battery cable
2. Start the engine and check for leaks. Correct as required.