Is it unnatural to say this in american english?

Yes, that sounds natural

That is the way we speak informally. It is not correct in standard English.

sabrynazulkyfly

"We're gonna be going to Texas tomorrow."

"gonna" may be said, but in writing it's "going to".

As far as "going to be going to", there are tons of examples in many books, not necessarily all American books either, so it is not unnatural at all.

See