Pulls hard and then quits...

I was merging on to I-5 this afternoon, there were no other cars on the on-ramp so I decided to gun it. She pulled hard through first gear, gave me a nice chirp going into second, shifted into third, and then at about 70 mph (appx. 3000 rpm) she just quit. Other than that, she runs like a top. Perfect idle, no dead spots, no hesitation even when flooring it on the highway from a 50mph roll.

This may be a dumb question, but what might have caused her to completely lose power at 70mph?:-k

It's a stock 400/727/3.23 sure grip except for the following modifications:

- Carter 9605S (600cfm), 0.098" primary jets with .074" x .047" rods, 0.090" secondary jets, 11inHg step-up spring (car has great vacuum, idles at 17inHg)

- Mild performance cam, 214 degrees intake, 224 degrees exhaust at .050" lift, .442" lift intake, .465" lift exaust

-Initial ignition timing is about 16 degrees btdc

- Full length headers

- High-flow air cleaner

- stock 1978 electronic ignition system, intake manifold, 452 heads, rockers, blah, blah, blah...

I'm not expecting to figure this out beyond a reasonable doubt, but any ideas on things that I can start investigating would be great.

Thanks FABO!