Why does my transmission not want to shift from 2nd to 3rd

Hi, Looks like you did first step for transmission maintenance of slipping but we need more info as engine light on? any code #s? type of trans? symptom? vin#? 4wd or 2wd ? engine size? ...etc... At this time it seems like we have more question then answers. I would recommend is to bring your TAHOE in so we can perform our complete diagnostic. It's the first part of any initial service and it's free of charge. thanks john