Toyota's and Nissan's have a closed circuit electrical system which means that you cannot adjust things like the speedo with a external programmer.
The short answer is that there is no way to adjust the speedo on the first gen tundras.
Hypertech sells a inline calibrator for the 07+ Tundy's but those are specific to that gen.
The other product you could try is the tru-speed by superlift but honestly in my experience these are a total waste of money and time.
You could also try calling a local tach and speedo shop but they will probably give you the short answer.
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Speedo adjustment on '02 Tundra 
Linear Mode
