For all you guys with ticking that happens intermittently, it is definitely your lifters. Regardless of the temperature of the engine, or the engine rpm, the ticking will continue to happen intermittently. I went through this trouble about 3,000 miles ago at 116,000 miles. After replacing the injectors and the cracked exhaust manifold, I knew it was the lifters. I was lucky enough to find a complete 4.0L rebuild kit on eBay for $100 that had everything I needed to solve the problem. While I was at it, I replaced the timing cover gasket, timing gears and chain, camshaft, headgasket, valve cover gasket, and exhaust/intake manifold gasket, and water pump gasket.
As far as replacing the lifters, it can be done fairly cheap if done by yourself, or it can get costly if done properly. Every book I read and everybody I asked said the camshaft had to be replaced along with the new lifters. That will run close to $200 for the camshaft. When replacing the camshaft, the whole grill has to be removed in order for the camshaft to be slid out. If replacing only the lifters, the (HEAVY) head has to be removed to access the lifters. If replacing the camshaft also, the radiator, fan, distributor, timing cover, timing gears and chain, and the grill have to be removed. Removing all of these will add considerable time(labor $$$) to the job. I was able to do the whole job by myself in a long weekend and that included 3 attempts at getting the timing right!!
Any other questions will be gladly answered.