I have a 2011 Dodge Avenger which is at 150K miles. Wanting to know about oil.

Any time you are draining the transmission fluid to change the filter always use new oil. Just make sure to check the manual and use a high quality oil that meets the manufacturers specs. Also be certain to follow the refill procedure to set the level at the right place. Unless you already have an underlying issue that you are trying to fix refilling the transmission with the proper oil to the correct level should not cause any issues. Have fun Clint