Hello i have a 98 gmc sierra with a 4L60E tranny and it is not shifting.. the computer gave a code that said to change the speed sensor but i did that and it still did not fix the problem. any suggestions?

Welcome to AF, and the code was, and what gear is it starting off in, 1st?, second, is it in default?

Speedometer working? If not then the sensor is still not working.
I ran into the same problem with a Ford Ranger. After market speed sensors would not work in it. I ended up getting a sensor from Ford.
Works flawlessly now.

Good luck!