One thing to check,
If you are having TPS ( Throttle Position Sensor ) issues, its not telling the trans when to shift properly because the TPS is faulty. Basically meaning that the TPS sends info back to the pcm regarding how far down you are mashing the gas. If you are at 1/2 throttle and the TPS is reporting 1/4 throttle then the converter on the tranny is going to not understand when to lock and unlock.
How long has it been since you have had your tranny serviced?
By serviced , I mean oil, filter and shift solenoids inspected?
2005 Supercrew F150 4x4
6" Rough Country lift
35x12.50x18 Nitto Trail Grapps
XD Monster wheels