I have a 99 SLS and am wondering if I can put it into a 99 STS? Does anyone know or has anyone done this?

Thanks!

Should be a bolt-in although I've never done it. From what I've read, they're the same engine and transmission--the main difference is the camshafts, which is not a player for the installation--although you might want to use the SLS computer too. Also, the radiator I got for my SLS was an STS radiator and it has oil cooling line attachments on the passenger side, and my SLS has a separate oil cooler hanging in front of the radiator and A/C condenser. So there might be some minor adjustments you'll have to make. Take into consideration that my SLS is a '95 and your cars are both 99's so a lot might have changed...

You'll have to swap the PCM with it.