Fear is driving this question. You say you would hate to break down with an infant. What's the actual worst-case scenario?
Walk through what the actual worst-case would be, step-by-step how you would handle it. Define specifically what you are trying to avoid. Now, how can that be avoided or made less of a crisis without buying a new truck? Is it even worth avoiding at all?
AAA and a charged cell phone are enough "cheap insurance" to cover most breakdowns. Keep an "emergency kit" in your car too (jumper cables, tire pump, water, snack bars, etc.). Doing all maintenance promptly and addressing issues as they arise (as it sounds like you do) are a good hedge against breakdowns happening in the first place. We drive a 2001 and a 2005. While barring flat tires, neither of these has left us stranded, I've had breakdowns with past vehicles, and AAA and charged cell phones were enough to fix the situation. Sure, it might ruin a day, but I'll take one ruined day and a good story to tell over spending thousands of dollars extra on a newer vehicle.
And, a decent vehicle will last a lot longer than 170,000 miles if treated right. My last car was a 2009 Hyundai and it quit at 261,xxx. Previous automotive death was a rusty ol' 1992 Buick just past 200,000.