Complete newb looking for help here. I know the problem is probably vague, but I haven't had time to really get the truck checked out.
2002 4.0L auto-trans 2wd
1) I bought it late last year with appx 106k miles. Filled it up the first time and reset the tripometer, checked it the next time I filled up and got about 23mpg. The next tank got about 16. Since then it's been steadily dropping to about 13. I basically drive like a granny, mostly just to and from work (4 miles per leg), but some of those tanks were non-stop highway at a pretty even 65mph down to Richmond to visit mum and then back up to the DC area (almost no driving in Richmond).
2) I got a tune-up only a few tanks after getting 16mpg which covered new fuel filter, new spark plugs, new wires (i think). That and a new battery basically fixed my starting problem, but didn't help mileage.
3) Twice in the months that I've had it, the O/D off light has flashed on my way to work. It wouldn't do it the next time I started it for the commute home, though.
4) Lastly, a few times mostly in the colder months on my way to work in the morning, I'd be at a stop light (in drive with foot brake pressed) and the truck would kind of pulse forward once every couple of seconds. Not very hard, but definitely there - almost like when you first shift into drive. I might be wrong, but it seemed like pressing the brake harder made the pulsing stop. The light would usually change soon after, however.
Any thoughts on possible causes, or if these symptoms are related? Mech buddy said it might be a torque converter issue, which seems reasonable to me. Thanks very much in advance for any help. The cost of gas and the worry that I might have an expensive problem are eating at me a bit.