i have a 94 k1500 with 6.5 and a 4l80e and intermittently it will just default to second gear. i then shut off vehicle and restart and runs good

Take a look at http://www.transmissionspecialty.com/parts/parts/34994-02K.htm

I am not saying that this could be you your problem but I do find their website very helpful.

//2000CAYukon