Those chips are a joke, they are just resistors or boxes that modify the data coming from the sensors before it gets to the ECM (jetchips is an example of this). You do NOT want the ECM being told it's 10*F outside when the actual air temp is 90*F, you'll have major problems, maybe even blow an engine.
You need a real tune that actually modifies the code inside the ECM, which is what we do.