Hey guys, got a problem. When I'm driving at 45-55, the RPMs seem to jump 150-200 and immediately go back down. It continues to do this for pretty much the whole time I drive at this speed in overdrive...if I am going up a hill, it seems to do this a little more often. Usually does it once every 10 seconds but when up a hill does it once every 5 seconds or so. If I'm going under or over this speed, I have no problems. I can cruise at 70 all day without any of this surging/rpm jump. I have an exhaust on this truck...so I can hear the change in rpm and I can see the gauge moving, but I can't feel an actual change in speed of the vehicle. It does this with the cruise control on or off. What you guys think?

201k miles
fuel pump and filter are fine
trans fluid at proper level
auto trans if you need to know

 

Lockup clutch in the Tq converter.. or selonoid..
Or TPS sending a fluctuating signal causing it to lock / unlock repeatedly.

 

So for the torque converter lockup clutch...is it going out? Why is it only doing it at that certain speed? If a solenoid...which solenoid should I be thinking about?

 

selonoid for the converter clutch inside the transmission.
Im not a big automatic trans guru but ive had that happen before on GMs. Not sure if you can unplug it and see if it quits on that year or not.
just by the way you describe it soudnd like the converter locking and unlocking, check your TPS output voltage for a steady smooth increase as you open the throttle, it may have a dead spot.
If not that im guessing the selonoid is going bad, its under the pan in there somewhere lol.