Sadly, it's unlikely to be something simple as a fuse. It's extremely unlikely a fuse would partially fail...they either work or they don't. Why do you think it might be a fuse? If it has the 4.0 OHV (pushrod) V-6, a common failure were the rocker arms and pushrods. Less expensive problems...

With an old car, there are host of things that could cause the problem. My guess is that the fuel pump is not at the top of the list. How long since you've changed spark plug wires? Fuel filter? The oxygen sensor? Pretty much every other part? Does it rev past 2000? Or just stumble there? -- Automedia's...