what is wrong when you pull the trans down to first gear and it shifts to second by itself. its a 4l60e. what im saying is i cant keep it in first, it stays in that gear about 2 sec and shifts to sec gear. when i put it in drive it shifts normal except for the harsh 1-2 shift, i installed a shift kit.

 

Did your vehicle shift to second when in manual first before the shift kit or is something new? Some computers will do this from the factory. Which shift kit did you install?