1988 ford f150 4.9 300 misses on occasion

Usually, the Exhaust Manifold warps and takes the intake manifold with it causing a vacuum leak. Since it's fuel injected, there's no chance of the old "rich-in-the-center" cylinders. At least once a year, you should check the torque on the exhaust/intake manifold bolts. The same fasteners hold both of them on to the side of the engine. The weight of the 2 manifolds hanging off the side of the engine, and the expansion and contraction of a nice cool intake manifold and very hot exhaust manifold cause the gaskets to fail. There's a couple of ways to fix it: Replace the Intake/Exhaust gasket and have the two manifolds milled together for a flush fit and replace all of the fasteners OR go aftermarket (if you can still find them) and get separate manifolds - preferably with a Stainless Steel Exhaust manifold or Header.