I have a 91 with the 3.0 and 5spd. Once in awhile (like 5 times so far) I'll be cruising along and all of a sudden it looses power for about a second and then its fine. It runs good and is giving no symptoms or warning. I happened to catch the tach once and the rpms went down from 3000 to 2500 and it went right back that was on the highway of course, although it has done it at different speeds. Keep in mind this all takes place within a second it's like hitting a bump. Has anyone experienced this before? It has a recent tune-up plugs, wires, oil air and fuel filters, and a PCV valve.

 

Have you considered checking your alternator, and/or connectors?