A few things here.
I'd suggest checking what the Oil Pressure actually is with a Gauge. There's two Oil Circuits for an Auto, the one for the engine runs at the lower pressure and that's the one that the Oil Switch is plugged in to and also where you should check with a Gauge. At hot idle, you'd like to see 15 PSI and running, around 50 PSI+.
If you find it's low, then check the High Pressure side (there's a test point on the Oil Filter) at 1000 rpm, in a forward gear you should get between 75 and 85 PSI and in Reverse, between 115 and 125 PSI.
If this second check is OK, then it's likely the engine is worn. If the second check is low, then it's possible the Oil Pump might be the cause, though given the mileage you have, it's likely the whole lot is tired.
I'd recommend changing out the Oil, to an ordinary Mineral Oil of 10W40 or possibly 15W40. That stuff you have in there won't be doing the gearbox any favours and could be the reason for burning so much Oil. When changing, it may need a good many miles and possibly a few changes to come good and flush that stuff from the engine.
< Edit to fix spelling! >
Edited by Moke Spider, 10 September 2016 - 09:07 AM.