I have a 2001 Ford Explorer Sport. I have 165K miles on it and as of this year it has been slowly falling apart on me. This year alone I have replaced the starter, radiator, ball joints and battery and now the transmission has went out. It will cost about $800 to replace. I have spent close to $1000 on it already this year. I am wondering if it would be best to just get something new or stick with this because it is paid off?

Stick with it. Most cars today can go 300,000+ miles, if they are well maintained. Typically, you need to replace lower ball joints, outer tie-rod ends, wheel bearings, struts, sway bar end-links, brake pads and shoes, and A/C compressors every 100,000 miles. Your transmission would've gone the distance, if you had dropped and cleaned the pan and magnet, changed the filter, and refilled with Mobil 1 Synthetic ATF every 30,000 miles.