Ride is jittery and squeaky after replacing shocks and struts

I picked up this car with only 30,500 miles on it that had very little uses for a long time. You could tell it needed shock/strut so I had new Lexus springs, new KYB mounts and new KYB shock/struts installed. I was looking forward to a nice long drive in my mint ride before putting it in storage for winter, however ride quality after the work was done is jittery and very squeaky. I made sure the part numbers were what the catalogs called for and inspecting all the parts and part numbers for any mistakes. KYB is the manufacturer of the Lexus genuine factory shock/strut and mounts so I thought It would be alright to mixing genuine and aftermarket parts to save a little over a third the cost on parts.
Are the specifications for aftermarket shocks the very same as the ones they are replacing making the ride jittery also why all the squeaking. Could the bushings be dried out? How can I fix these problems?

Thank you,
Dave