My Stangs buck'n like a mad cow

Hey guys, I was wondering if any of you have had this same problem. I've got a manual trans, 98 GT that has been bucking on me lately. It feels almost like disengaging and reengaging the clutch sometimes while on the highway and other times from a standstill start (not racing or anything) its hard to control the bucking (almost like how I drove when I first started learning to drive stick years ago).

A little more background: I had it in the shop about 3 weeks ago because it was making this sound like a twang (springy sound) when I shifted. The guys at the shop couldn't recreate the noise but found that my rear was leaking oil. Now I have this bucking problem and I wonder if its related to that twang.

Anybody have any idea what this could be or have you had a similar experience? Let me know.

Not that I have noticed. I usually notice it when i'm starting out, shifting gears or even on the highway. The car only has 36,000 miles on it but I'm not the original owner either. I was suspecting the clutch earlier too but was hoping I could get some other people's perspectives.

Also, I didn't mention that I installed some screamin demon coils in the fall. I think I burnt a couple of plugs and am due to replace them. Do you guys think this could be the culprit?????

I'm gonna see if I can check the tranny fluid level, but if that's not the problem that sux - it sounds like I might need a new clutch.