1993 Chevy Truck

Engine Performance problem
1993 Chevy Truck 6 cyl Two Wheel Drive Automatic

Ok so I really need some help figuring out why my truck runs the way it does. First of all when I start it up when its cold and let it idle for a few seconds without revving it, it will sound like the rpms will drop lower than the idling speed and shake violently and die out, other times it will drop to a really low rpm and shake and sputter and it will go back to the idling rpm.

When I take off from a stopped position with the rpms a little above idle it will seem to go good, but then down the road (without changing the rpms) it will completely lose power and will start to hesitate and skip. It seems like the further I press my pedal down, the longer it will skip. Sometimes it sounds like the engine was shut off for a few seconds and then started back up again. The pedal does have some hesitation, I will press it and a second or two later I hear the engine rev. This happens when I'm in gear driving, but doesnt happen while i'm idling in park. Theres a complete loss of power when I go up hills, I have to put the pedal down to the floor, full throttle, wait about 4 seconds of skipping and then I will start to gain some speed when going up hills.

I've replaced the distributor cap, spark plugs, spark plug wires, new converter, manifold, y-pipe (huge rusted holes in this, I thought it was interfering with the o2 sensor), and the whole exhaust system behind the converter. I checked my vacuums visually and there seems to be no leaks.
I wonder if a bad o2 sensor could cause this?

If you need any more information just ask me, I'm very confused and I really want to figure this out. I've also heard that chevy's timing chain goes at about 100k miles. My mileage is 82k
Any help I would greatly appreciate it.