[Thomas]

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In addition to the above suggestions, I would also check your spark plugs.. I had a similar problem when I opened the exhaust up on a car and allowed it to breath better.. The car did not want to run above 3,500 RPMS without backfiring and missing.. Plugs can do funny things and act differently under different driving conditions or RPMS...

I would suggest running NGK plugs.. Guys on the site here convinced me and it was the best plug I ever had run.. I use them in both my big block motors..

Rich

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I can get it to rev beyond that RPM range in first, so I do not think it is ignition related. I will not rule anything out though.

The one thing I did not try was to do the same "speed test" while driving along in 2nd or even 3rd and then going up one gear.

As I was doing this on a public road, I am always concious of trying to keep things resonably safe.