The long crank time is classic low fuel prressure.
Test the pressure with a gage on the fuel rail fitting for that purpose.
Do the test after the truck has set enough time you think the start will be difficult.
Attach the gage first, then switch ignition to 'run' only, do not crank.
What is the gage reading?
If below about 20 psi, cycle the ignition several times.
What is the pressure?
If not up to at least 35 psi, you have a pump issue.
Low pressure at the beginning of cranking will extend the crank time until the pump builds full pressure.
Don't waist time on spark plugs etc because it won't help starting.