hi, we have a 1993 gmc sierra truck, 6.2 diesel. when its cold it will shift only to 1st-2cnd gears until it warms up then it shifts to od, its fine for about 15-20 miles, then it won't hold into od. when we disconnect the 2 wires on heat sensor, it shifts fine & holds into od when its warm, but won't shift into od when its cold. we changed fluid & filter. we appreciate any help. thanks.

 

Not real sure but you'd probably get more help in the Silverado board.