Hi guys. I have a 88 vl sl auto standard 3.0l. Jatco 4 speed. The jatco is off another vl that had 100kms and was mint in that car we put it in this one. Now its holding the gears. It wont change gears till 4200 rpm between every gear and even 4th overdrive wont change till 120kph I have checked the vac line between manifold and box. Seems ok. Can someone help in what it could be. I had been told it could of been the coolant temp sensor. I replaced that still the same. I tried another auto ecu still the same. Any help would be much appreciated. I just want it sorted and shifting smoothly. Thankyou in advance

CTS won't affect the Trans, it only sends resitive feedback to the engine ECU. The transmission has its own temp sensor but normally only locks the box out of first or top gear when the oil gets real hot. Grab/swap the Auto trans computer from the donor car. the one under the dash cover next to the drivers right leg.

Have done that. Same thing. Could it be a temp sensor on the side of the box or the modulator

I would lean more towards the modulator I would think, as it was working fine before removal from the donor vehicle. Did it get dropped or hit at any time? I would be inclined to get the box serviced or grab a filter kits for it and give it a flush. Maybe one of the valves inside are semi clogged with crud. Out of my league I'm afraid, apart from replacing the valve body to a full manual version. Al's Glides does them in NSW for around $600. It's easy to R&R them, takes about 30mins.