2010 GMC Sierra 2500 HD Q&A

2010 GMC Sierra 2500 HD Question: My truck is stuck in high gear. Any suggestions why?

My truck is a 2010 GMC Silverado 2500 series HD . I would like to know some reasons why the truck is stuck in high gear. -
Answer 1
Is there any codes in the ECM and/or TCM. Post the codes that we might help. Possible convertor locked up. -