My ranger sport 2003 runs grat cold but coughs and sputters really bad when under load and warmed up. Fuel filter and pump have been replaced

 

Welcome to the forum

I would test compression first, just to take that off the table or you can waste alot of time and money on non-fixes if it is a compression issue
Cold engine
Remove all spark plugs first, inspect the tips of each and keep them in order 1 thru 6
Test compression and write down results
2003 3.0l should show 160+ psi in each cylinder but depends on gauge and battery condition(cranking speed)

But the results are what you are after, not "high numbers"
The PSI numbers should be within 10% of each other

3.0l like most engines will get burnt valves over time, that's why there has been a fix called a "Valve Job" since the early 1900's lol, it happens on all engines with valves
Starts as small compression leaks and just gets worse over time


2nd is to inspect the coil pack, coils are low impedance devices so can show heat sensitive issues, i.e. misfires after warm up
Look for cracks in the top, bottom and sides of coil pack
You can test a coil pack with OHM meter, but can only test if its bad NOT good, so a test will show a bad coil but not if its good, it can still be bad when in use, lol

You should have misfire codes, P0300 to P0316
What are they exactly

And any other codes?

 

 

No other codes?

If not then wasn't a fuel issue, that would have set lean or rich codes

Do a compression test
Have a look at #5 spark plug tip(P0305) and compare it to #4 and #6 tips