88 Ranger runs rough and smokes

I have an '88 Ford Ranger, 2.9L 6 Cyl., Auto, about 100K on it. When weather got cold, it began to run rough when cold, but would smooth out and run okay when warmed up. I figured it needed a tune-up and was planning on doing so this winter. However, it now appears to be an ignition problem, in that I do not think it is firing on all cylinders. When last started, it dumped un-burned fuel into the exhaust system, which then leaked out of the muffler. Before I start replacing "stuff", was hoping someone could suggest a few things to check first.

Any help would be greatly appreciated.
Gillman