I just finished the rebuild on my 03, 4.0. You did not say which engine you have. For the 4.0 it is recommended that you use the special timing tool kit. It costs about $150.00. It locks the crank in place and sets and holds the cam's in position as well as holds the sprockets while you torque the bolts. The work is not hard, but getting to the chains requires removal of almost everything from the engine except the heads. I did mine as port of an overhaul of the engine. I can not imagine doing this job with the engine still in the truck. Access to the back of the head is limited. That limited access and not being able to see what you are doing would make it a really tough job. Even with superior mechanical skills. With the engine out, it's not a real big deal. I followed the directions in the manual, except I had already installed my rockers. An interesting point is that when I set the cam in position, it actually stayed there with out assistance, or need for the locking tool. I did however use the tools. With that much disassembly required, you might as well replace the bottom end parts and freshen up the heads and gaskets. Ps the timing kit is expensive. On mine, the chains and sprockets visually looked good, however the plastic parts were just about all broken, with a lot of the bits stuck in the oil pickup.
