Can I replace my 3.6 liter engine with a 3.8 liter?

In theory you can, but in reality it would end up costing more in the long run. Just bolting things up can be a real challenge when using two different engine sizes. PLus the way they operate is different where the electronics are and valve train is concerned. This was only used in the Lacrosse and Impala if memory serves me right along with the 3.8. Can I ask what happened that lead to the diagnosis or a bad motor?