Probably nothing needs to be replaced.
I would clean the MAF sensor and IAC Valve, either can cause poor engine running after warm up.
Is there a CEL(check engine light) when you first turn on the key?
There should be, and it should go off after a few seconds or when engine starts.
If no CEL then bulb could be bad or system is bad.
If no CEL at all then I would check if there are any trouble codes
You can check the codes yourself have a read here: Ford Ranger - Testing EEC-IV Equipped Engines
MIL = CEL