Full tank of gas how many miles can I go on a 2003 Tahoe???

This would depend on fast you drive but out on the highway at 65 or so I would expect 300 to 350. (Assuming the Tahoe is in good shape)

Are you towing any thing , how fast , highway or city? Any where from 200 to 350.

in 2021- i have 2006 tahoe with 80k miles (only) and i filled up in CA for $115.00 and it got me 300 miles on the dot until the check engine light came on. i drove conservatively and most of the time was on interstate

Until it stops ....