I loaded a new tune and my truck seams to go into 4th gear and lock the converter up at the same time then unlock real fast. Other time it seams to work normal (goes into 4th then locks the converter up like another gear)? Does it have to be at a certain speed or gear for the Torque converter to lock up?

 

At WOT it locks up 2 seconds after it shifts into third gear or 0 seconds if it's a 99-00 model.

At part throttle it's variable and can lock up shortly after the shift into second if the truck isn't seeing a high calculated load or anywhere in between up to the third gear shift at WOT depending on the load.

If you hit the brakes it come out of lock up. Also, if you downshift into second at WOT it will come out of lock up under the factory settings.

 

So what would you think would cause it to lock up right as it shifts into 4th and then unlock right away? This is only going at slow speeds, part throttle. This is a 2002 Lightning and only started doing this when I loaded my new tune.