Buy one immediately!
Like this week or today...
I'd recommend the Haynes manual if there's one available for your Tahoe. You can buy them at Autozone or on line like Amazon or eBay.
You're flying blind without a manual and driving yourself nuts in the process. Plus starting multiple threads on the same subject with the same questions that can easily be found in a repair manual isnt helping you or us.
You need to get
a lot more familiar with your vehicle than you are at present unless you simply plan to outsource everything to a shop, even things like oil changes. For example, you werent sure if you needed to pull the transmission pan off to inspect the flex plate. A manual would have answered that question for you.
You dont need to worry about major repairs at first, just start at the basic maintenance (fluids, filters, brake jobs, simple diagnosis like reading oil, fuel pressure and vacuum, etc.
You have a code reader so being able to pull codes is covered. But you need the manual to know how to complete repairs based on whatever goes wrong or if/when your tahoe generates codes.