Possible Rear End VIBE?

I am having a vibe problem with my car.
I now have solid motor mounts and installed them due to thinking my stocks ones where bad. The vibration was there before the motor mount swap and has not gotten better or worse after I installed them. So it now seems to be coming from the driveline and not the motor. I have a new tranny and clutch as well as aluminum driveshaft. I have put a little over 6000 miles on all 3. When I 1st installed my aluminum driveshaft I could tell right off the back how great it was especially on the highway. Now I cant even tell I have one anymore because I have a vibration and it feels as if it might be my rear end itself causing it. The vibration occurs the most between 2800 - 3200 rpm. When I take off I have a slight shutter at times and it feels as if I loose a little bit of grip then regain it. Almost as if I am driving in the rain and take off on a painted line then the tire spins on the line and gets its grip back once off the line and back on the road. Hopefully you can understand what I mean by that. I also feel like I have lost power because of it. Should I install new hardware onto my driveshaft and possibly a rear end rebuild? This is driving me crazy!

Thanks for the replies guys! I installed 8 plug wires covers today. I noticed one of my MSD wires had a mark from where it was burning near the header. I did a full tune up on the car about 4 months ago. Hopefully these Taylor plug boot covers will help keep things cool against miss fires. I am gonna put my car up on a lift soon and check out all of the driveshaft hardware as well as for play with the rear wheel bearings. Its been a while since I had my tires balanced so I am just gonna go ahead and get that done at a shop. Hopefully things will get better.

I drove my car today with the Taylor plug wire boot covers and the car ran great. No more misfire once the weather was in the upper 90's. I also put the car in 4th gear at 30mph and hit the throtle all the way and there was no slippage on the clutch. So I still need to check the h-ware on the driveshaft once the car is on a lift which wont be till my next day off. Oh and the wheel bearing play check as well.

So if all of my driveshaft hardware is fine and I still have a vibe, then it could be my rear end? See........about a year ago I blew my tranny and put in a new one. I am wondering if any damage was done to the rear end???? I also have a tranny question and hope one of you can answer it. When I got a new/rebuilt tranny for my car put in, I am assuming the shop put in a 90-93 tranny. If they put in a tranny rebuild from another year, would it matter?