This is an evaporative emissions system concern that will need hands on troubleshooting following shop manual instruction.
Everything can be fixed, but you'll need a technician with proper equipment to test the vehicle and find the cause of the concern.
RepairPal Certified shops can diagnose and repair your 2008 Toyota Tundra. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.