Ok - I just found this thread and joined the forum just so I can reply to this. My 2004 deville has 217,700 on it currently and I do NOT consider this high at all. The day I bought it with 62k on it I fully intended on taking it to somewhere between 350k and 400k before selling it still running good. EVERYTHING with a northstar has to do with proper maintenance. I use Mobile 1 Extended performance 15k oil and change it every 6k to 8k miles. Don't use fram paper oil filters - use the supertech from walmart or the Mobile 1 filter - both are very comparable actually as they are fabric, high-flow filters. Switch to the K&N air filter, change your fuel filter every 30k to 50k miles, flush your anti-freeze/coolant every 60k miles or so but IMMEDIATELY get rid of the Dex-cool (that's first priority - did it at the dealership day I bought mine and replaced with Prestone Global). Change your plugs using original iridium plugs every 60k to 75k miles. At 9 years old and nearly 220k miles my car is literally as smooth as it was the day I bought it and looks new in and out. I can look down into the oil fill and the engine look as clean as new inside. There should be absolutely no reason to not get another 150k out of her. Take care of your cadillacs and you can drive them about as long as you'd like. I still get the same gas mileage that I did when I bought it (which with the air filter and fluids listed above is 31 mpg highway at 70 mph). I floor it routinely to keep the carbon out of it as well about once every 2 weeks taking it up to 90 or so very briefly (from current highway speed - never from stop or lower spead as this is aweful for a car). Also, the use of a fuel injector cleaner is extremely helpful - I use Lucas Oil for this every 3rd fill-up and only use good quality fuels. I also strongly recommend changing your transmission fluid and steering fluid every 60k to 70k miles also and during this I add 2 quarts of lucas trans fluid (normally 1 but the pan on this transmission is an 18 quart pan). The 4t80e transmission will ALSO drive as long as you want to drive it as long as you change the fluids and treat it well. I should point out that this is the routine I use on all of our vehicles and we almost NEVER have any car problems and I strongly recommend it. I think that Amsoil would likely be as good or better for any of these fluids, but I've had a working process with easy accessability to the ones I use so I've stayed with the ones I currently use. I LOVE cadillacs - have all of my life, grew up with them and have seen even models that were considered garbage run fantastic for years and years (mid-80's 4.1 - never had issues with them) when maintianed well.