Harder and harder to start

Tell me what you think...

'99 Mercury Mountaineer, V-8 5.0L engine, 98K miles.

Lately she's been getting harder and harder to start. As in not REAL
hard, but she cranks for a good 2 seconds before she catches. Once
running, no problems. No recent changes in engine performance or
MPG's. But, gradually and consistently taking longer to start, in all
conditions. Battery's real strong, so that's not it.

I've put in new double platinum spark plugs, had the fuel filter changed,
had the local shop perform a fuel-injector cleaning service, replaced the
air filter, cleaned out the throttle body (it had the sticky accelerator pedal
problem which is now cleared up), put in some fresh Mobil 1 5W-30 and
a new filter.

I even bought her some new tires then told her how pretty she looks...

No change.

Any ideas?