Torque converter doesn't lockup but different then you think

[ericem]

Hey guys, this 92 touring wagon was suppost to be my parts car. I plan on swapping the whole engine and tranny into my sedan. Here is the thing though. The tranny doesn't lockup on the highway so 100+ km/h. It does actually lockup, but ONLY 1 time for 5 minutes. After 5 mins of driving locked up, unlocks. If you stop and restart the car will lock up, and again 5mins.

Otherwise shifts fine, AWD works great, no torque bind, all gears grab solid, just not locking up on the highway sucks as it uses much more fuel. Should I just try replacing the fluid and thats it?

[Legacy777]

Any codes in the ECU or TCU?

Speedo work I assume?

[ericem]

yup and no check engine and no power light flash on startup and the lights do work. Going to replace the fluid though.

[ericem]

Did the transmission fluid change definitely shifts alot better and when it changes gears doesn't act like it didn't fully engage like before. Seems good, didn't drive it for long enough to test the torque converter lock up on the highway. Hopefully it works fine, regardless going into my sedan!