After looking at the the small cubic in. differences on these motors I believe I just stick with the 3.1 since the stroke & compression are the same as well as the cam specs. I might possibly look more into taking out the current 30k motor and do the intake swaps as mentioned above, the comp cams MPG/torque cam, and doing the head gaskets, and getting a good tune. Thanks for getting back and confirming on the possible problem of the head gaskets that I had heard about too.

 

yes you can i am a student at scc and i put a 3.4 engine and tranny from 2005 monte carlo into a 2003 pontiac that had the 3.1 lt, i was going to you the 3.4 pcm but the theft mod wouldnt allow the car to start, so i had to put the 3.1 pcm back in and it started right up

 

You probably needed the VIN updated in the 3.4 PCM and then a security relearn.
Nice way to boost a little performance, remove the 3100 and drop a 3400 in it's place

 

I ran my 99 Monte Carlo with a 3400 swap on the stock 3100 PCM for three years with no issues and plenty of power.I was even able to pass my yearly New York state inspections which require that trouble no codes be present.. Its just the bore size that is different between the engines,The stroke is the same so engine timing is basically the same,the PCM is able to compensate some for air/fuel ratio needs demanded by the slight displacement increase..some may disagree with that but from someone who has done it and had no reliability issue for over 50k hard driven miles i say its fine to run it like that..Is it a perfect tune for optimum performance? NO..But a stock 3100 PCM will adequately run the vehicle until you can have a custom tune done and you will definitely notice a large power increase over the 3100..