I thought that the SES light would always set a code. Is this a 1500 truck? Does it have a 4L80E transmission?
Are the ground connections ok? There are 2 or 3 that bolt to a stud on the back passenger side of the intake manifold. When those were off on mine it screwed up a lot of stuff. (transmission wouldn't even shift)
(I have a 93 k1500 ext. cab 6.2)