Moms Merc. Mountaineer....5.0L V8

Problem:
Takes a while to get started, usually has to crank for over 5 seconds. (Compared to my truck that's a lifetime). Runs great though

Recent tune-up done:
Plugs/wires
Fuel Filter
TB clean
MAF clean
IAC clean
Fuel injector treatment through tank.

It's been doin this forever, just kind-of annoying. Could it be a coil or what?

 

Every time you start it, or just on cold starts? Looks like you've got most everything covered. Maybe losing fuel pressure as it sits?? Bad O-rings on the injectors may cause this....

 

Does it 90% of the time. Thanks