Car will surge around 45 MPH under mild load when in over drive. RPM will jump up and down about 250 RPM. Also may notice this with cruise on and going up a hill. Other speeds my also have this problem.
Basically the TCC switch is not being fully engaged causing the torque converter to go in and out of lock up
The purpose of the TCC solenoid switch is to signal the transmission to drop out of torque control lockup when the brake is applied. There is a simple test to determine if the switch is properly adjusted. Using your right foot on the gas to maintain a steady 50 mph, apply the brake with your left foot (not enough to slow the car) and observe the tachometer. If the RPM'* increase by 300 to 400 when you apply the brake, and drop back down when you release the brake, the TCC solenoid switch is properly set and doing its job. If it does not react in this manner, refer to this thread:
Remove the panel from under the drivers side dash. There should be one thumb nut above the gas pedal and 3 more bolts along the dash. This may differ on some years.
Once that has been disconnected you will need to remove any wires connected to the panel. The OBD2 lifts out after uncliping it and and the small light comes out with a twist.
Now remove the fuse panel and blinker.
Now look above your brake pedal and you will see these two switches. The bottom one is the brake lights, and the top one is the TCC switch.
Looking behind the brake pedal you will see the plungers for the switch. These need to come on at the same time.
So lets remove them and test them. Give the switch about 1/8 turn counter clockwise and then pull the switch out. Then unplug the plug, be careful not to pull on the wires.
Do the same thing to remove the top switch.
Now take the switch to your work bench and test it with your DVOM, Turn the multimeter to the lowest ohm setting and attach the probes to the terminals as shown here. This is the brake light switch.
You should show infinity. Now press the plunger in all the way, and you should have a reading.
Now take your TCC switch and connect as shown.
You should have infinity, press the plunger in and you should have a reading.
Now connect the TCC switch as shown here.
And you should have a reading.
Now press the plunger in all the way and you should have infinity.
If all this checks out, the switches are good. If not, replace them.
Now reconnect the plugs to the switches, don't worry, they only go in one way.
Then put the switches back in. You will see here that there are grooves in the post. This is so you can adjust the depth of the switch.
Put the switches back in and check alignment with a mirror.
Put everything back together and put the panel back in place. If you still feel any surging, adjust the top switch a little. by moving it in.