Put a new fuel filter in it and check the fuel pressure.
Set your base timing to zero degrees at tdc with the distributor reference wire unplugged.
Check out all of the normal tune up parts, cap wires plugs etc.
Look for vacuum leaks.
Get a spray bottle of water and mist the coil while its running, also take a look at the coil, if you see lines of grey colored residue in the corners, the coil is bad
Make sure your egr valve isnt stuck or has a hole in it.
Make sure the egr passage in the throttle body isnt plugged full of carbon
Use a timing light to look at the injector spray patterns while its running.
Look at the ground wires going to the intake manifold especially the two that are next to the temp sensor
The headers are not going to cure the problem but it aint helping either.
Do you get a check engine light and have you looked for any stored codes?
TBI performance issues are due to carbon crud, bad ignition parts, dirty or leaking throttle body, vacuum leaks, lack of fuel pressure, bad grounds, bad ignition control module, bad distributor pickup, bad or worn distributor, bad egr solenoid, bad map sensor. Etc..
So the answer is, it could be anything above, it could be all of the above.
But it is all bolt on parts. You just gotta figure out which parts and then, and this is big, you have to reset and recalibrate those parts.
You can bolt bolt a brand new everything onto these engines and they will still run like crap because you havent "reset" the system.
Its all pretty easy to do it just takes a bit to wrap your head around how the TBI works
