88' 300 TE Wagon with hydraulic shock trouble

[cdp3456]

I just put new hydraulic shocks on the back of my 88' 300 TE Wagon because the seals were out and leaking. The car felt good for awhile but now when you are going down the road at about 50 to 70 it feels like the car is jumping around on the road. Like you are towing something. You seam to be fighting with the car to keep it going straight down the road. You can feel it more when my boys are in the far back seats. I have flushed out the system and put new MB oil in it. The oil that came out was black and now the new oil in the reservoir is on the dark side. Could it be the height control valve or did I miss something. I did put new struts on the front last fall because of pot holes in Michigan.