2000 Sunfire not accelerating

Hi everybody,
I have a 2000 sunfire (2.2) and lately, it's been having a weird problem with acceleration. It's a manual, and the RPM's, even whilst going at a steady speed, will randomly jump up, then fall back down, and the engine sounds like it's running fast, but not getting the power. As a result, my acceleration has become really really slow, because when I start from a stop, my RPM's jump, but it takes the car a second to "catch up" and start moving. On the freeway, going a solid 70, my RPM's will move from 3500 down to 2500, and back up, and it almost sounds like the engine/trans is struggling? Hard to describe. The car shifts and drives, but it's just starting to sound like "the little engine that could."
I'm not sure if it could be related, but I've also had some problems starting it for awhile. The engine won't always turn over the first time, and sometimes it needs gas or for me to let off the clutch at juuuust the right moment for it to start.
If anyone has any ideas on what this could be, I would greatly appreciate it! The car has 120k miles on it (orig. engine and trans.), yet I'm really really hoping it's not a failing trans/engine, cuz that would be rather expensive. Friends have suggested that it might be a failing relay/sensor, so I'm hoping that's it...

Thanks in advance!!

the only thing i could think of would be the top end. i.e. fuel injectors, spark plugs, valve seals, all that good stuff. my friend had a kind-of similar problem, not quite to the extent of yours, but he bought some f.i. cleaner and it works just fine. it probably doesnt have anything to do w/ the tranny though. nothing would make the rpm's drop and rise like u described if the tranny was failing.

Just to update so maybe this can help other people - I took the car to a trans shop, and they verified that yes, I need a new clutch. :( *sad* So, I'm looking at around $700 worth of work. I thought (and so did the trans shop) that it would still be ok to drive on for awhile, but no such luck, it's sitting in a parking lot down the road right now. Oi. Thanks for the help, though. Injectors was what everyone else thought it was, but I just had a new fuel pump put in not long ago, and they were cleaned then, so I had a sinking feeling it would be another big, expensive problem.

Bah... bring it to me and i'll do it for 350. Its not that hard just time consuming.