1989 Ford Ranger... I added a can of seafoam, changed the fuel filter and spark plugs and it still runs horrible. I dont know what else to replace

First hook up a fuel pump pressure gauge to make sure there is enough pressure to start the engine.
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Check for spark at the spark plugs.

fuel filter,air filter.

You need to run a electronic engine control fault code test to see what is in memory. To do this test and see meanings of codes received go here.

HAVE YOU EVER SERVICED THE FUEL FILTER ? EVERY 30,000 MILES ,"DEFINE JERKING REAL BAD" IS IT A STICK SHIFT? ANY OIL LEAKS COULD BE GETTING ON CLUTCH. AND CHECK ING SYSTEM COULD HAVE SPARK JUMPING

Old fuel in tank, fuel filter clogged, plugged/clogged carb. or fuel injectors.

1. Drain fuel from tank and replace with new fuel with SeaFoam or Lucas

2. Repace fuel filter

3. With engine running at a high idle and air cleaner off, spray or pour carb/fuel injection cleaner into carb/fuel injectors.

If problems persist, check plug wires for cracks and/or breaks. Pull spark plugs checking for fouling.

low fuel pressure comes to my mind.

Check to see if there are valve/header issues.

I agree. Try replacing the spark plugs, install new spark plug wires, change the air filter, change the fuel filter, and test the battery and alternator. Run a bottle of fuel system cleaner and water remover through it. To replace the spark plugs you'll most likely have to go through the wheel wells cause of their hard accessibility from the top. The fuel filter is located on the inside of the frame on the driver's side. Hope this helps. God bless

change fuel filter and add a can of SEAFOAM(parts stores) to a 1/2 tank of Premium gas. Try it. and when you do, look inside the fuel filter and see the goop that's causing most of your problems. your vehicle suffers from EGS

change fuel filter. add can of SEAFOAM(parts house) to fuel. It sounds like the beginning of EGS(ethanol gas syndrome). corn liquor substance, water, and clogging. all caused by ethanol fuel.