Starter issues

[Billdozer2]

Hey guys, with the snow storm coming up to the NH area today, I went down to the truck to start and move it. When I turned the key, the starter would spin but it would not engage the flywheel to turn the engine over. I'm assuming it is the starter solenoid, but I'm curious what others think. Battery voltage is good and the wiring seems ok. Also, every time I've replaced a starter in my lifetime, on a car or pickup truck, I've always replaced the complete starter. Mostly because you can only purchase a starter as a complete assembly. But after doing some searching on the forum, I guess I could replace just the solenoid itself. Any advise, tips, concerns with replacing a starter other than "Don't drop it on yourself."?

I also want to add that I knew something was going on with the starter as last week, when I would turn the key, there would be a split second delay before the starter would engage the flywheel and turn the engine over. It would turn the engine over normally. It wasn't slow or anything and it only happened a couple of times and seemed to go back to normal after a couple of days.

Truck is a 2013 Volvo w/ISX 2250 and 427k miles.