I have a 97' K1500 w/230 K miles and is bucking like a bad miss at highway speeds under load such as going up a hill. The bucking seems to deminish if I back off the accelerator. The engine idles fine w/o roughness or miss symtoms even if I accelerate slowly. This maybe related to surging while accelerating from a standstill problem I've had for a while. Any ideas ? BTW - engine seems to accelerate much better when cold when it is probably in open loop control.