The new Tailgates that we have can be used as a tailgate. I haven't gotten my hands on any but other vendors that have used them stated they were not the flimsy crap you normally get. Doors you get what you pay for, generic fit cheap parts are going to deal you fits, and GM isn't making them anymore... If it didn't come on the truck expect to spend some time fitting it, or expect to take it to a professional to fit it. This is true for every panel.
General population has the thought that everything should just bolt up in place with no work to be done, this just isn't a reasonable expectation. There is a reason why the 73-87 trucks didn't have perfect fit gaps, they weren't necessary. Drop by a body shop and get their opinion on factory vs aftermarket, they will generally tell you everything requires work to get a good fit.