Steven

186000 miles is not that many.
First B230F designation is not a turbo, right?
Second, The vibration at 1400-1500 occurs while in neutral[also for AT], yes?
I'll assume that it occurs both in neutral and while underway, same rpm's.
I'll also assume that it is more of a slight vibration, than really BAD.
If it is really bad, your engine is coming apart, hope it is not that.

My best hint from you was "I took it for a drive and it does seem to have the slightest hesitation when accelarating hard"

If the slight-vibration is only engine related, I would first check for bad vac-hoses on the intake-side, then, second have someone check the fuel pressure at the high-side fuel-manifold. Reason 1400r's is where vacumm increases and if the fuel-pressure regulator is not getting good vacumm it will not deliver the correct pressure increase to the injectors and give you a small hesitation/vibration. Even though you can highway accelerate smoothly.
Fix bad hoses and if the pressure stays low or fluctuates [line pressure is around 36/43psi., high press is 50/60psi.], try a new regulator first $24. A fuel pump is $600, don't go there, yet.

STP injector cleaner [gold-stuff], actually works +, can be helpful.
Fan clutch goes out around 2400r's, but when that goes bad, you really know it.

Otherwise my b230ft has a very small vibration at 1500 with 240000miles, no rebuild yet, still running fine. Welcome to the high mileage B230-club, keep on truck'n.