The 1998 Corvettes have a steering system called "Speed Sensitive Steering". It sounds to me that you may have a mis-match of components and are lacking the correct Electronics/Hydraulics to make it function as intended. What Speed Sensitive Steering does is reduce the Power Assist at normal operating speeds for better driver road feel and increases the power assist at low speeds for better mobility (ease of handling and parking). Also, the '98 Vette uses a rack and pinion steering gear system, and unless you've changed it, your 69 Camaro has the old style 800 Steering Gear system. If your steering system, outside of the power steering pump, is still the original, I'd recommend that you install the original power steering pump. That should make life a lot easier. The 1998 Corvettes also had another option available called "Active Handling" which I doubt that your donor car had, but if it did, there's a whole different set of hardware/software issues involved with that steering system.
