My 2011 Tahoe will start and when I put in reverse the check engine light will come on. I noticed I can see the sections of gears on the dash but it will not show me a line under the gear I choose. I am able to move through the gears as needed but it bothers me that I cannot see what gear I am in. Any suggestions on the issue?

 

Getting all 4 code families read is step one so you can see what the computer system is seeing since you're getting a CEL.
That will give you a starting point on what to check.
Reading ALL the codes is step one in any repair shops diagnosis, today's vehicles are computers on tires.