That's Liembach's esc, it always works in mix mode, can't turn it off for individual ch function like the choice you'd have with a Sabertooth.
I'd move from Aux 1 to Aux 3 so the knob will give proportional control for/rev. Then Aux 2 used for steering.
With the 3pos switch centered on Aux 2, it should drive straight, and up or down should steer lt/rt... is it doing that?
I was using some 9amp Banebot esc's for pump control, but Robotmarketplace no longer can get them. But this one from E-flite seems to be a suitable replacement and even has a lipo cut off should you choose to use one... although the lower voltage of 9 to 12.6 will slow down the hyd speed vs a 10 cell @13.4v fully charged.
http://www.robotmarketplace.com/products/0-EFLA105.html
Then setting up the mix on the radio is super simple & will extend batt run times greatly not having the pump run wide open all the time.
