1993 Trooper 3.2 sohc

Ok so i have been paying close attention to when the torque converter is locking. It seems to only lock up when the car is cold and over 50-55 mph in 4th gear. It also only locks when im giving it 1/4 - 1/2 throttle..The converter locks when the throttle position is increased... If i back it off so the car wont actually be increasing speed, it unlocks and when i completely let off it unlocks. Once it fully warms up, it doesn't lock up at all. When it actually locks, i have keep the throttle pressed and hit the brake to make sure the switch is working and it is, the converter unlocks when the brake is bushed. Fluid looks great and it shifts great too. No lights on the dash either.

Any ideas?