strange vibration after manifold swap

[68jimmy]

Well I finally completed my manifold swap this past weekend. I had a factory aluminum q-jet manifold that I replaced with a new performer 2104. I went thru my 1406 edelbrock, adjusted the floats, installed some leaner jets, and replaced the gaskets. Figured while it was apart I'd replace the hei cap, rotor. Once that was all done I fired it up, set the timing, tweaked the carb and took it for a spin.
First thing I noticed that the new manifold really woke up this motor. the second was now a vibration that starts at about 30mph. It doesn't feel like it 's coming from the engine, although when I let off the gas it seems to go away and starts again when I press the accelerator. After getting back home I re-checked my ignition wires to be sure I had the firing order correct. I discovered that my #4 plug wire to the hei cap was *%^# which kept it from snapping onto the cap. I figured that must be it and that I was getting a miss on one or more cylinders. I ran and picked up a new set of wires, installed them and took off again. Same vibration is still there.
What's weird is that this vibration was not there last week prior to all this work. A couple of months ago I did replace the carrier bearing, but I did not have time to get under the truck and check it yesterday...
Anyone have a similar experience after some engine work? The engine is a 350 with a th350 behind it.

Thanks in advance!

donovan