Fuel can go bad if it has a lot of headspace for condensation to form and fall in the fuel. If it was stored with no head space it should be okay but why take a chance for what it costs.

It sounds like your ball connector for the throttle is worn out and needs replacing.

As far as the screw on the throttle going loose tighten it I have never had this problem and its obviously designed to not do this. Is the carburetor barrel stiff so that when the arm is moved it loosens the nut? If the truck sat dried up oil can make it sticky. Another possibility is that its not set at the right position and the servo when the throttle is closed the servo can still move (but the barrel can't) forcing the arm to move making the nut come loose. This could also be why the ball connector is coming off.