With 145,000 miles, have you ever changed your Oxygen sensor? That is probably the cause of your lousey gas mileage. Your post and others on here that I haven't found again since I registered with the intermittant performance issues remind me of the problems I had caused by a series of poor quality Throttle Position Sensors. Thst sensor can casue serious problems. If you pull off the connector, the engine won't start at all, that is how important it is to the computer. Both of these items are often overlooked, so maybe they are worth looking at, you probably would get to them, but with gasoline prices as they are, an O2 sensor is worth changing on a regular basis. (O2 sensors fail to RICH, they are designed that way, if they failed to a LEAN condition, that would cause overheating and maybe self destruction of engines.) Hope this helps.