It's related to the transmission. First thing to do is make sure the ATF (automatic transmission fluid) is full and clean. Park the car on a level surface, pull the transmission dipstick and wipe it off, reinsert it, pull it again and check the fluid level and cleanliness of the fluid. The marks on the dipstick give you the fluid level, and it should appear a nice reddish color. If it's low and dirty, it could cause your issues. You can also look at getting a transmission flush and filter change, which should cost you around $100. You want them to drop the pan and change the filter, not just change the fluid - do NOT take it to a place that only vacuums the fluid out (like Jiffylube). (just FYI, some filters in a trans can only be accessed by a rebuild but don't worry about those just yet) - I'd start with checking fluid levels yourself, then - if you have to, proceeding to the flush/filter change service.