bad_ls1

I have a 98 ls m6 trans am. Having a small issue with the check gauges light coming on around 6,400rpm and staying illuminated until shifting. Valve train is upgraded thanks to btr .660 springs, retainers, push rods, trunion upgrade as well, before someone says its over revving when i know for a fact it can handle it safely. Has a new alternator and new battery of this year. Speedo reads correct, tach reads correct, voltage does not drop when the check gauges light comes on, great oil pressure reading, and gas in the tank, so I'm not sure why this light only comes on at 6,400rpm until i shift. Any help would be great.