That sounds more like a problem with Castor and Camber rather than with the Power Steering; especially if it feels like you have that "Driving on Top of an EGG" sensation. Just as in the design of Old Wagon and Buggy Wheels ...In order for ANY vehicle to essentially steer itself in a Straight Line... The tops of both wheels need to be tilted ever so slightly towards one another.
When absolutely "Straight Up and Down" or "Bowed Outwards"... Either Front Wheel will Hunt for a different track, depending upon the Angle of the Road Grade and pull in the Dominant Direction and will only be able to ride Straight and True when the Vehicle is temporarily riding on the very Top of any Road Crest. IIANM The "TOE IN" Angle on our SUVs should be "0". Others may know more and can correct me here on that issue.
Regarding your ability to "Turn the Wheel with a Finger"... That condition cannot be expected when Non-OEM Power Steering Rack Hardware has been installed. FWIW... The Detroit Axle Company sells their Re-Man Units with Lifetime Warranties and with updated Components and care that will rival GM OEM Power Rack and Pinion Steering systems.
I mention this from personal experience with having used several replacement units from them and they in fact DID return that sensation of "Being able to Turn the Wheel with One Finger" in a very satisfactory manner. You might want to visit this link and compare the one you used as a replacement against what they sell and look for any glaring hardware differences to the one you installed:
www.detroitaxle.com