Sister's '04 Jeep GC did the same thing for a long time. TC would go in and out of lockup also, with associated jump in rpms. TPS finally got so bad that it threw a code. Apparently, there's some threshold value of failure it has to exceed before it throws a code. TPS was pretty cheap at RockAuto.com. $28 or so, IIRC. New TPS fixed it.