Hey guys, my ecotec cavalier with the auto tranny is acting up a little bit.. lets say im doing 80kmh on a relatively level road surface with no bumps in it.. my car will hold 3000rpm lets say to maintain 80kmh, which is fine. But suddenly itll drop to approx. 2500rpm for a second or two and the car slows down.. then there is a wierd grinding/popping happening somewhere in the front end that you can hear and feel which lasts about 1 second (it feels like you hit a bump in the road but theres no bump there ), the grinding stops and then it raises back to 3000rpm, speeds up, and holds this rpm for a bit .. the cycle of normal-rpmdrop-grind-rpmraise happens once every 10 seconds or so and it gets more pronounced when you hold the RPMs while going uphill.. whats wrong with my poor cavalier?

3000 rpm, you should be doing way more than 80 kmh. It sounds like your 4th gear is messed up, and popping in and out.

How many miles you have on it?

Hey guys, the 3000rpm thing was just an example. I can go out and give you an accurate number if you'd like. The tranny has 140000kms on her, shes nowhere near new but shes not old enough to fail I dont think? Tomorrow I'll try driving around in 3 to see if its popping in and out of gears, since in 3 it shouldnt try to upshift or downshift like it does in D. Also I had my tranny flushed about 20,000kms ago, would that affect anything? Thanks guys!

Make sure the tranny's not leaking at all - low fluid level can cause all kinds of problems.
Transmissions can fail much sooner than 140,000km, depending on how they're treated. Although these are typically fairly robust for what they are, I've seen transmissions dye in as little as a few thousand kms when abused (or less, depending on the severity of the abuse).
With a jump of 500RPM, that does sound like a gear going in and out. If it was less (say 150-250RPM), I would maybe guess at the torque converter clutch. This may also engage with the transmission in "3", so trying it there may help to identify something.
The tranny flush SHOULDN'T cause a problem, unless they caused something to start leaking (see first comment). Even being down 1 litre can cause very erratic behavior with some automatics.

Wow John, thanks for the detailed reply! I'm almost positive my tranny isn't leaking or I would have seen some tranny fluid in the snow where I park but I'll pay more attention from now on hah.. I'll be lucky if this is the problem since otherwise it sounds like my trannys about to blow..
Honestly I drive my Cavalier nicely, I rarely ever beat it up, the things never seen a neutral drop in its life, etc.. it spent about a year commuting 100 kilometers every day with 5 people in the car, though.. I imagine the tranny wasn't too happy with me then.
I'll pay attention to the exact RPM dip if a difference of ~200rpm means a totally different problem, and I'll definitely try driving around in 3 tomorrow to see if this helps anything. Maybe I'll drive around going 1, 2, 3, D, instead of keeping it always in D? Is this bad for my tranny?

you dont need to switch gears maunually.....if that even stopped it, it would just be a band-aid. did it do this before you had it flushed? and was this the first time it had been flushed?

The car had absolutely no problems before the flush and yes this was its first flush.. also I noticed that on the highway I've developed a really wierd problem.. you know how in a standard car when you screw up a burnout you get crazy wheel hop and the entire car shakes up and down violently? Well my car does that, but a little less severe, cruising down the highway at 120kmh at 3000rpm at random intervals. It only lasts a couple seconds then stops, then a couple seconds then stops, etc with no bumps in the highway. wtf is wrong with my car?

So today was the coldest day of the year so far (rediculously cold) and my tranny wasnt acting up as bad as it usually does. Maybe my tranny fluid isnt the right vicosity? somebody help!