x2 as above re pump.
Man I would try a few more things before assuming it is the fuel filter.
Stumbling below 2000 rpm....something is not right. -Have the codes read with a decent scanner even if if there is no CE light, by returning to place that did motor? they must have scanner.
If you are taking out the IAC and cleaning the port, do the TPS (throttle position sensor ) as well, which is located directly above the IAC. (white/yellowish connector)
It has a tang that has to be aligned, you will see it when you remove it. Mark the TPS with marker line across housing and TPS.(easier to install again)
Fuel injectors/fuel system cleaning-I use Chevron Techron fuels which contain techroline.
For that added cleaning, you can buy Techron in a bottle. This will clean the system well.
The bottle only covers just over 11 gallons so you can add two bottles to a full tank and take it for a good highway boogie, after cleaning the IAC and TPS.
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For pump lubrication twice a year I add some Lucas fuel treatment to the fuel with the techron. ( a few oz only)
http://www.lucasoil.com/products/display_products.sd?catid=2&iid=26
This is also good to use on new rebuilt as top-oil.
As a new rebuilt, I would also take plugs out myself check gaps & plug type and see how it is burning.