I recently replaced the water pump on my 2002 4.0L. Afterwards it has been shifting jerkily into 2nd from 1st and often from 2nd into 3rd. I don't notice any difference on other gears. The only things that could have been affected by the maintenance was disconnecting the trans cooler when the radiator was pulled or when my Dad disconnected the throttle position sensor and wasn't sure if he put it back on right. The sensor might have been spring-loaded when he removed it. I need to take it in for a transmission fluid change. It's probably on the original except for the 4.5qts I changed when I replaced the AT filter when I bought it in April. It has 141k miles on it now. So is it in need of a fluid change, sensor is on wrong, or is something broken?

 

turned out to be a broken throttle position sensor