You can check your owner's manual supplement, the Toyota Passport to Performance (scheduled maintenance guide). If you have lost it, you can look it up here:
http://smg.toyotapartsandservice.com/ (US)
http://www.toyota.ca/cgi-bin/WebObje...?o110000e.html (Canada)
If you go to Toyota USA's FAQ site,
http://toyota.custhelp.com/ , and search for "timing" you can find this document:
Timing Belt and Timing Chain:
http://toyota.custhelp.com/cgi-bin/t...i=&p_topview=1
which tells you if your 1990-current Toyota has a timing belt or timing chain. (Your 2002 Tundra has a timing belt.)
Timing Belt Maintenance:
http://toyota.custhelp.com/cgi-bin/t...i=&p_topview=1
Since you have a Toyota that is newer than 1999, then you should replace the timing belt at every 90,000 miles or 6 year intervals. (Older Toyotas should be checked at 60,000 miles/4 years and inspected at every 15,000 miles thereafter (but to save on costs, it may be better to just do a 60,000 mile change interval instead of the 15,000 mile inspections).)