Intermittent longer than normal starts:

[Rum Runner]

(1999 Ford Ranger 4.0L V-6 2WD 177,000 miles)

Need some help from the ones in the know. The above truck was running ok a few months ago. I changed the oil & filter and went ahead and had the fuel filter changed. To my knowledge the fuel filter has never been changed. After the new fuel filter was installed I started getting "intermittent longer than normal starts". Recently it has become more regular. The truck is not a regular driver and may go a few days without being started. I keep the fuel tank full and it never gets below 1/2 tank. Could it be old gasoline? A weakened battery? Any and all comments are welcomed.

Truck history:
New IAC valve 115k miles
New crank sensor 145k miles
New Bosch fuel pump 150k miles.
Non-ethanol fuel used since 100k miles.
I'm not the original owner.

 

[Uncle Gump]

I know my truck starts way better when the battery is topped up. The battery tender was money well spent.

Do you have a fuel pressure gage?

How you tried cycling the key a couple times to ensure the fuel system is fully primed?