had the same problem that you are having would be driving on the highway and then my RPMS would drop to zero and everything seemed normal just that the engine had died out so i pulled over got out and knocked on the dizzy a few times then cranked it right back over then about a week later i was driving and the car just died completely and after that i replaced the dizzy and everything worked fine agian and i havent had the problem since its been about 5 months
things to look for
tach jumping when driving
slow acceleration from stop to go
Check
Fuel
Wires
Rotor/ Cap
check for spark ( you might still have spark if thats the case make sure that the rotor is tightned down just make sure the screw is in the shaft because that happened to mine where it came out and the cap was still on there and i was still getting spark but it was firing at the wrong time and wasnt strong enough so that is what i would check first is your rotor)