Yes. However, you are responsible for ensuring any cargo or other items you have in the bed are secured.
yes it is legal to drive your truck in Texas with the tailgate down.
As long as it does not obscure your lights or license plate you can drive with your tailgate down.
Yes.
Not only is gas mileage not improved by driving with the tailgate down or removed, it gets worse. Counter-intuitively, driving with the tailgate down increases the aerodynamic profile and wind resistance, degrading fuel economy. (Mythbusters recently debunked the myth. See link.) See the Related Link for "Mythbusters Episode #43" at the bottom left.
yes
Queens Drive is the name of a street in Lincoln, Nebraska. Q Street is the name of a street in Omaha, Nebraska. Quarry Oaks Drive is the name of a street in Ashland, Nebraska.
Binman drive garbage trucks.
Trucks are used for carrying supplies and to just drive.
tailgate
Yes -- either that or there are an awful lot of trucks breaking the law and getting away with it. Trucks can't drive on are parkways but expressways are fine.
About 45 minutes.
In the US at least half the people drive trucks, so some of them must own logging companies. Owners of very small logging companies might actually drive trucks at work.