I have a 2000 Dakota with the 4.7, automatic and 80k mi. This is the first auto I've had in over 20 years. The ones my wife has had have been front drives. Now that we have cold weather I've noticed that the transmission won't go to torque converter lockup until it's good and warmed up. The fluid level is good and it doesn't look or smell burnt. Is this a normal thing with these trucks? Thanks.