Russell,
Chevron used to sell a product called Tractor Hydraulic Fluid. It was used in rigs that had a common sump for final drive, hydraulics and transmission. The viscosity of this product is about a 10 weight. ATF is slightly thinner...sort of a 9+ weight. If you are using a product like the Tractor Hydraulic fluid, you can see that the viscosity is almost the same as ATF.
This would mean it isn't the viscosity of the fluid in your PS pump that is causing the slow response, but lack of volume (GPM). You said it was a small pump from a Ford Escort. I think you have pegged the problem.
Stuart
