this is something i wrote for another post, so part of it works for you, but im too lazy to rewrite it:
As a tuner, I have to disagree slightly with some of what’s being said. Yes to what has been said about changing muffler won’t need a tune. The factory tune is capable of changing the LTFT/STFT to adjust for the free flowing muffler. When you change the CAI the MAF frequency does need to be adjusted in the PCM to correct for the now smoother, uninterrupted airflow. Again the PCM can adjust to accept the change to the CAI, but you will be on the ‘edge’ of what is programmed in the computer.
What this means in simple terms, since we are talking about S10s, GM made these trucks to be able to run from Alaska to Death Valley. There is that much alterations that can be has in the computer tuning to adjust for the elevation and type of fuel grade in the tank.
When you change things like the muff and CAI you’re going into the limits of those left and right factory GM perimeters.
So, again in simple terms, you can take a bone stock S10 and go get a dyno tune for your vehicle at your location and you will pick up HP/TQ numbers without changing any parts. Because you are specifying I am going to drive in this location with this fuel. The tuner takes that information and tunes your PCM to your specs, which shortens GMs wide left and right perimeters.
Now, you add a good exhaust, CAI, good spark plugs, high flow cats, your engine is now breathing freely your PCM won’t be able to fuel it with the current factory GM tune, and you’ll get a CEL.
So, in closing, if you add/change anything from the factory specs, you will benefit from a tune. This is best done on 1998 and newer vehicles do to the change in PCM.
Also a tune, isn’t just engine, if you have an auto, they can be tuned as well.
Tunes aren’t cheap. Don’t call or email and get a $300 mail in tune and consider it done. A mail in tune needs to be data logged, and multiple changes need to be made to be 100% completely tuned.
Except to pay at least $500-750 for a legit, dyno tune on an S10.
Hope this helps.