you could get a new motor. it would cost around 3k-5k for a 2.5 litre. depends on what you mean by easy install. if you are mechanically challenged you can do it yourself.get a bentley manual, label all the hoses and wires you take out, get a cherry picker and .......etc. if you want to convert to a manual, you would have to get 5spd tranny and every other assessory with it. none of this is easy stuff. you dont sound like you know what youre doing so, my advice is to bring your car to a shop and find out whats making your car slow down alot and fix it.
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