I've been trying to suss a fix for my excessive driveline hum and vibration that happens only when 4th gear kicks in on the auto, at 75kmh, fades away when you start taking it over 87 to 95kmh. A test drive by a mech showed the torque convertor causes it when it locks in, and makes the car act like it's a manual, that is going too slow for it's highest gear or something, labors until 90 kmh.

Well I was driving my sisters EL Futura today (mines an EF Fairmont), and I noticed her auto's lock-up happens at 60kmh, in economy it goes into 4th at 60kmh. And the driveline is quiet an responsive. My 4th kicks in at 75kmh, and is noisy as hell. Why is it kicking in so late, any thoughts.

like the mech said it is the tourque converter it could be slightly damaged

Maybe its an ex-chaser car or has an ex-chaser ECU in it.

I like to keep the selector in 3rd when staying at 60kmh for long periods. I've been doing it for about 2 years, but all that does is make it rev higher for longer. On my sisters car when it goes into 4th at 60k's shes silky.
Maybe this practice of mine has killed the torque converter or something else?

timmeh should be educated about slightly worn torque convertors

Heh, my bro's old EF does the same, dead on 70km/h.