I recently drove my van to FLA. Previously I replaced the two VSS in the trans and the rear. I did this because I felt it was not shifting into OD. As I made the 900 mile trip the van seemed to upshift around 55- 65 MPH and the RPMS would decrease significantly creating a better fuel mileage. My nephew said that it was probably the torque convertor locking up. It does not do this all of the time during regular driving and has me puzzled. Are there any checks I can do to confirm this? Is it an electronic part? Should the convertor lock up at regular highway speeds? Any advice is greatly appreciated.

You guys are great and helped me with the past OD issues which I fear may have not been the issue to begin with.

Thanks

 

A significant drop in RPMs is more likely due to the OD kicking in and not from TC lock up.

Lock up occurs when you're cruising at a fairly steady speed, such as when on a flat highway. While holding your foot steady on the gas pedal tap the brake pedal with your left foot. Turning on the brake lights will disengage the lock up. If you can feel a change then the lock up was working.