Speed related vibration

What to consider and where to start troubleshooting a speed related vibration on a 2002 Tacoma Xtracab PreRunner pickup?

The truck vibrates between ~65 mph and ~75 mph. The alloy wheels and tires have about 8K miles and are recently balanced. Goodyear Forenza tires are at 32 psi. Vibration is sometimes accentuated when on long highway curve but is not consistent. There is no vibration below 60 mph.

Rotate the tyres from the front to the back. If there is a change you will know it is one or more tyres and or wheels. If not then you have another problem, maybe a suspension part that is worn.

In conjunction with what Joseph said, Alignment check and balance recheck would be my advice.