dieselenthusiast

I just bought a 2000, 4.0, auto, XJ with 168.000 miles on it. The vehicle is in fairly good physical shape; however, maintenance was seldom performed other than changing the oil. So to make a long story short, the transmission fluid doesn’t look like it has ever been changed. (Yes, the trany fluid is dark brown, basically the color of used motor oil). I bought the Jeep knowing the problems; although I didn’t mind paying a fairly small price for a fairly nice XJ. I tried doing a search and found that one possible problem could be a bad throttle position sensor. What other possibilities are out there? Also, what are the chances that my Trany is going bad and my OD is toast?