My truck isn't shifting correctly? I believe it's code E76 comming up

What is your question?

It's not shifting correctly! If I stay close in the neighborhood I'm ok there isn't a problem but when I go on the highway or expressway it's a problem it won't shift it's code E 76 I believe

What makes this problem better or worse?

Going slow

How long has your 2007 GMC Envoy had this problem?

A few days