torque convertor no lock up

Hi there I have a 96 pontiac sunrunner and I am having a problem with the 3 spd auto transmission not locking up once I am up to speed/tempature. The weird thing is that it locks up when I first hit the hiway each morning. After I slow and or hit the brakes it will not lock up again untill the vehicle has sat for at least 8 hours? So far I have done a bit on trouble shooting. I have power coming through the brake pedal switch to the TCC relay. I have power coming through ECM to the TCC relay[ I put a light bulb in line to check this, It did seem a bit weak, what should the voltage be coming out of the ECM 12v?] Is there a solenoid/switch inside the tranny that activates the TCC? If so what is the procedure to change this switch. Any assistance would be greatly appreciated. than you!