My check engein light will still come on randomly, always at highway speeds. I have replaced the Oxygen Sensor and borrowed a TPS off a 90 PU that doesn't have this problem, and it still happens, and my TPS is fine on the other truck...any ideas what could be wrong with it? BTW, is it possible this is because of my Hypertech Thermomaster chip? I am supposed to run Premium, but always run regular. I have heard this will make the computer retard the timing, so I think I will take it back to stock...hopefully that will help...any more ideas?