Here is something that may help guys with Vortec trucks, that don't want to have to change to an LS1 style box. He runs a 4.3L S10. George is one of my NHRA stock Eliminator customers, from down in Louisiana:
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If you don't have the distributer right in the right spot it will act like a rev limiter. http://www.youtube.com/watch?v=OsE9OSm2UdE This was when I was trying to figure the problem out. You can hear what sounds like a rev limiter around 5400rpm. http://www.youtube.com/watch?v=PBM4SjJzZOE Here is me shifting at 6000 rpm with no problem. You have to grind off the lockdown tab and make it adjustable. I made a degree plate for the top of the distributer cap in 1 degree amounts. I then retarded the distributer a little at a time untill the problem went away.
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George Roussel Jr. 4262 1996 S10 p-q/sa
He has not checked the retard on a scan tool, so I don't have any numbers for that. He just retarded the distributor (which houses the cam position sensor) until it went away.
Hope this helps somebody. George said to go ahead and post this.