What is wrong with my car?

Car has significant lack of power. Top speed was about 75 with poor acceleration past about 45 and degraded over about 20 mins of use to 35 mph (lower when going uphill). Engine check light blinking. Squealing noise also occurring both at idle and when trying to maintain speed. Some vibration also seems to happen, but not sure. Rpms seem to come up a bit every couple mins for a few seconds, but then goes back. New spark plugs, new battery and new ignition coils did not help this issue. Fuel pressure was also checked, but was running at 35 psi. Vehicle is 2002 Ford Crown Vic, 8cyl 4.6L