The EPA estimated fuel economy for a 1989 Chevy S10 Blazer (the Tahoe was a trim level, not a separate model in 1989) with the 6-cylinder engine varied depending on the transmission (manual or automatic) and whether it was 2WD or 4WD. You won't find a single, precise number.
Expect figures in the range of 15-20 mpg combined (city and highway). Highway mileage would likely be higher than city mileage. Actual mileage will vary considerably based on driving habits, vehicle condition, and terrain.
