Sluggish 200 Malibu

The old Malibu (2000, V6, 3.1) just turned 100,000 miles and feels sluggish when I hit the gas. The RPM's jump between 2 and 2.5 (up and down, giving a gentle feeling of jumping) when I gently accelerate, especially on the highway and uphill, but seems to speed up okay when I hit the gas harder. Plugs, sensor problem, any other ideas?

Fuel filter, catalytic convertor, o2 sensor?? Get it scanned for any codes?

100k is a good time to get new wires and plugs, notice , wires also. Get DELCO
ONLY, Nothing else :nono: All the other stuff mentioned above plus a " top engine cleaner " like SEAFOAM , no carb cleaner:nono: you have to use throttle body freindly cleaners, no silicone spray unless it says ox sensor friendly. Hit the MAF with some seafoam or throttlebody cleaner also. Seafoam i just saw the other day at advance auto parts. It comes in a number of forms liquid and spray. The liquid you pour into your upper intake manifold while the engine is running , remove the big vacuum line that goes to the brake booster, pour slowly if the engine stops and a cylinder fills with liquid, you can bend a rod + this does not clean your throttle body. I like the spray, you can still squirt in the manifold, just remove the red straw or it will get sucked into the motor like i did.:frown:
how does the car run cold ? if it is the same I would eliminate the 02, when the car is cold the o2 is to unrliable till it warms up so the car runs off i think the VE tables in open loop.

Thanks for the tips, I'll take a look!