Best bang-for-the-buck, BB tune as mentioned. Also as mentioned, first be sure everything else is up-to-par. All the normal maintenance items that are due for your Tahoe's mileage: Trans fluid, rear diff oil, coolant, brakes, hub bearings, suspension bushings, spark plugs, air filter, clean MAF, fix major leaks, etc. Fix any issues that cause an SES light if it's on or comes on intermittently (not so important in this aspect if it's something that doesn't affect a tune). If the upstream oxygen sensors are over 100K miles old, they might could stand replacing. Fresh sensors reporting accurately will ensure a dialed-in tune.