99 Ranger engine trouble

I have the 4.0 in this thing. Yesterday I noticed a problem with it. When I was leaving somewhere to go home, the engine lost a bunch of power and started to stutter for about 30 seconds and then after I hit the gas, it fixed itself. It took it a bit to respond though. It happened a second time yesterday also. Same situation. It seems to be doing this about 2 minutes into the drive. Sometimes it seems to run roughly at start-up. I'm guessing it's the O2 sensors because by the book, I'm 8,000 miles overdue. It says do them at 120K but now I'm at 128K. This wouldn't be a fuel system issue, would it? Full tune-up done very recently.

Are you getting an engine light?

Whatever the problem, its probably not the oxygen sensors .... as you have heated sensors and they are pretty tough.

Water in the gas could be possible, had you just put new gas in or almost on empty.

I don't think it's the O2 sensor. does you vehicle idle OK and runs good on the freeway. Any check engine Light indication. If the problem occur only during startup I would suspect the Power Control Module (PCM). when first starting, the PCM operates on a default setting until after a set period, normally after the engine reaches a certain temperature. So essentially, the
O2 sensor does not even get into play until after that time. Check your enginee coolant temperature sensor. You have two, one for the gauge and the other is an input to the PCM. The sensor you want is on the right hand side of the block above the water pump. (I also have a '99 Ranger 4.0L)