I've decided I'm going to post all of my problems and solutions in threads, I've found that this is the easiest thing to search for, for others with similar problems.

Problem:
As it has gotten a bit colder, my 97' w/ 160k developed a lumpy, rough idle. Never stalled, but would shake and shutter at low speeds, such as sitting in traffic. Under light acceleration I experienced hesitation and erratic RPMs, and surges of power. No CEL, but two codes for misfire on cyl. 4 and random misfires.

Solution:
New upstream O2 sensor and spark plugs. (O2 sensor had never been replaced, spark plugs replaced last at ~125k)

Hope this helps someone, sometime.