1991 Cadillac Fleetwood My Caddy has a diagnostic code of e

Hello, my 1991 Fleetwood caddy has started to drive badly, when I put it in drive it pulls real hard until it gets up to about 10mpgs and then its fine, the dia. Code e-40 (power steering pressure open) appeared and since then i've changed the fuel filter, the power steering pressure switch, the distrubuter cap and button, wires and spark plugs, i've even put in sea foam to see if bad gas may be the problem I also sprayed the throttle body down with fuel injection cleaner after all this I still get the code e 40 what should I do next i'm at a wall now wondering whats my next step thanks for your help!