Guys, I need some opinions on something.  I drove the Vette this morning to my hometown of Yakima, WA for the funeral of a family friend.  Yakima is about 3.5 hours from where I live, Vancouver, WA.  Car ran like a top the whole way except there was an "occurrence" when I was about 20 miles from my destination.  I was cruising on a freeway, going about 70 or a little more when it suddenly started surging and cutting out.  Then there was a loud backfire.  I pushed the clutch in and started pulling over thinking the engine would quit and I was done, but it stayed running.  I gunned it a few times, put it back in gear and continued driving.  I kept it under 60 the rest of the way there and it ran fine.  Any thoughts???

What year car?  Why would the tack go crazy when the engine ran rough unless it is an electronic glich.  At first I was thinking trash in the gas, stuck float, etc.

Dave, many years ago I had a similiar problem with my MGB. I lost a screw for the distributor points plate. Of course, it fell right into the garage floor drain sump. I figured no problem, just get another screw. I put the screw in then later drove the car. The car acted like yours. When I finially made it home I checked the advance plate in the distributor. Sure enough it wouldn't move because the new screw was a little longer than the original one. I had to shave it down for my advance to work. Another thought could be that your fuel filter is plugged or your gas cap vent is plugged.........if you have a vented cap. I sure hope you can at least drive home at a slower pace to then look for the problem. 

Dave, what kind of ignition system do you have?
It sounds like one of three things, or possibly a combo of all. Either the coil is in the process of taking a dump, the ignition module, or the pick-up coil.
I would at the very least change the coil and ignition module before making the trip back home, if at all possible.
Take the cap off, and have a look up inside of it, looking for anything that looks like spark damage, corrosion, or melting. Take the ignition rotor off and look at the bottom of it, and see if you see any lightning bolts going fromt eh center, out towards the two screws that hold it on. Check the little carbon "tit" in the center of the cap for breakage, or other damage.
ANY problems with any of these parts will lead to coil failure, and coil failure will lead to module failure.
Make sure all of the terminals on the coil that fit into the cap, where the wires plug in are seated properly, and that the 4 screws that hold the coil into the cap are nice and snug, but not too tight. Definitely make sure the ground strap and dogleg terminal for the coil are present, and connected correctly.
Hope you have tools to do all of this on the road....

Back in June I had the plug wire to #5 cylinder burn up. It didn't happen immediately, It took a couple of weeks to become very apparent what was wrong. Car started having a rough idle, then it would stumble under hard acceleration, eventlualy it started to backfire through the exhaust and I could feel it under my feet. Checked the timing, carb, etc. Started checking plug wires and there it was; it had burned through the insulation right at the boot connection. New plug wire and problem went away. Mind you, I have headers on mine and that is what burned up the wire. I see you have the cast manifolds so heat shouldn't be as much of a problem. Looking forward to the solution...

Thanks for all the suggestions, guys.  First of all, pretty sure it's not fuel or one individual cylinder.  What I felt was a complete cut-out on the primary side of the ignition, reasonably sure.  And when I said the tach was going crazy, I meant it was dropping down to zero and then bouncing back up to normal RPM's during the cutouts.  So to me that sounds like complete loss of voltage on the primary side.  

Ignition modules are electronic...they can fail in many ways. You're right in that they do usually fail when hot, completely, and then work fine again when cooled off. I think you're on the right track, however, with the coil/connections. And..you know how I am about "new"....it don't mean diddly! 
Cap/rotor/coil/module failures can occur at any time, and rarely do they fail close to home. Double-check all of the connections at the dist, too, including the 12v power in connection, the connection for the module, and even the tach. A loose connection at the cap can cause weird stuff, too. Hope the coil takes care of it...or at least gets ya back home safely. 

Thanks for the vote of confidence, Joel!  Interesting you mentioned the tach connection.  For about 1/2 hour before the incident, the tach started acting funny.  It read low for a long time (2500 at 70 when I know it's more like 2900) but sometimes it would bounce around between the two.  I figured it was the tach filter that needed to be replaced - the board is brand new (yep, I know what you think about "new, though).  I'll make sure that connection is solid before I get on the road.  Just waiting for the auto parts store to open.  

Well, there's a new cap, rotor and coil under the hood now and a module in the front seat, just in case.  All connections are solid and the car is running good.  Tach is steady at 3K and above.  Probably won't know until everything is good and hot, though.