I have a Sierra Series.1 XR4x4, 2.8.

On a run, up until about 10miles, it runs and pulls great, but then it starts to falter, as if there is a
faulty plug-lead, and it seems to miss, and won't pull cleanly.

The coil doesn't get hot, so that side doesn't seem stressed..... Recent new cap & rotor.

I've got a set of new plug-leads coming, but I just wondered if anyone recognised this behaviour, and
could suggest what else I might check.