I'm still rockin' my Aug 2000 OEM battery. I attribute its longevity on the ease of starting.
Key on, pause, clutch in, less than a second of crank, release and she's running. Every time.
If I were in your situation, I'd go ahead and replace it before this winter. There's no telling when it'll fail (and you KNOW it's gonna be the worst possible time when it goes). I've never had to push start this truck, but I guarantee it's not gonna be fun, especially alone. $50 well spent, just for the peace of mind.
I keep a jump start unit in my truck (it was a gift).