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Discussion Starter #1
1996 Impala SS, 41,000 miles Florida car, Hypertech Pro, K&N, shift kit, 160F thermostat.
When running out to redline, there is a slight hesitation or roughness at between 5,000 rpm and 5,500 rpm before it automatically shifts. Anyone have any ideas? thank you.
 

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I had similar issue with my 96 SS. Check Ignition Control Module and optispark. I had both issues showing up with dyno tuning at high rpm. Replacing both put the "umph" back in the motor. I used an optispark from Summit, their brand, it failed with less than 5k miles on it, on a 383 rebuild at 250,000 miles. Replaced with an OEM rebuilt optispark, my mechanic procurred, no ignition issues now. I ran the original motor with the Hypertech "tuning", didn't notice much difference in performance, but the settings for thermostat and tranny shifting and rpm limits made the shifting firmer.
Have you removed the Hypertech tuning, and run it without that tuning as a test? That would be a quick and no-cost test before you delve into ignition component replacement. The factory tuning should allow you to get to redline, if you still have the roughness, it's not the Hypertech.
 

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Discussion Starter #3
Great suggestions. Thank you.
I'll try removing the Hypertech, but other than shift points, gearing, speedo recalibration, I thought that the main benefit was being able to run premium gas. I have already turned off shift firmness because I have a shift kit.
But I will try removing it anyway. How can I test the ignition control module and the optispark. Or do you just need to replace them and see. And where is the ignition control module located? I can see the optispark. Just replaced the squeeking serpatine belt after 25 yrs!
 

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The ICM is located on the driver cylinder on the same bracket/heatsink as the coil. If you still have 25 year old plug wires I would very closely examine the insulation on them as that stuff does dry out and rot at some point.

-Brian
 

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5k "stumble" if often Opti related. It may be as simple as just cleaning it as oil or coolant get in it from either a wearing opti bearing or weeping WP and that crap will get in the very tiny slots of the reluctor wheel the optical sensor sees
 
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