Do you have the Diesel or the 3.7 Gas? If it is the 3.7 Gas use 5w20 as recommended in the car manual. As far as Oil, there is an API rating, SL, SM, SN. SN is the most recent also look to see that they oil is Chrysler certified 6395 I think. Anyway depending on what type of oil was being used in your Lib before for example the Dino Oil and want to switch to Synthetic you have slowly move it to do so. You could go 4 qts Dino 1 qt Synthetic, then next change 3qts dino and 2 qts synthetic. Try and stick with the same brand. I use Penzoil Platnum 5w20.
I wouldn't put any additives like injector cleaner or the Oil. Also change your spark plugs every 30K use the copper plugs not the platinum. It would also be good to do a coolant flush using only the Mopar brand and lastly you should do transmission flush and have your transfer case and have the axle fluids checked changed if needed. If you only do local driving, once in the while take it on the highway go up to hwy speed then just open it up and blow some carbon out if it.
When you get knee-deep in a situation, floor it.