87 cuttin out and engine light on

[snacob14]

well, I took out my new truck (87 R10 350tbi) got it out on the highway up to speed (70mph) and about 20 miles into the trip it started cutting out a little and the check engine light would come on. If I stopped it and restarted the light would go away and it wouldn't do it. But then on my return trip it started doing it again. Any ideas? Looks like the wires and plugs are fairly new, but thet plugs were light a dirt brown and looked a little marred up on the diode.