No RWD? Get the transfer pressure checked. If you got pressure the clutches are going bad. If you have no pressure the transfer valve is bad. I changed mine myself
The AWD system for the svx is 90/10 or 50/50. The front wheels always have power but the rears wheel will vary. The amount of RWD depends on the pressure to the transfer clutches. This pressure increases in reverse, 1st, if slippage is detected (that is front /rear) and under rapid acceleration and when the ABS signal is detected but it doesn't apply brakes to the wheels.
From what you say the rear wheel drive is going out. Do not load your tranny up until you get it fixed. You will damage the front dif and axles.
The SVX drive system can not put 100% power to any one wheel. The best it can do is 25% to any wheel when the AWD tranfer pressure is at max. Except for the limited slip rear end. That could put 50% to one of the rear wheels but only when transfer pressure is max.