Sorry, I keep responding to my own thread like this. I don't think it is the clutch. 2nd gear has very little harshness (bucking or shuddering), 3rd, 4th, 5th have none at all (since I wasn't starting in 3/4/5). Also, reverse is perfect, no shudder or shake. If the clutch was to blame I'm almost 100% sure I'd feel the same vibration in reverse as I feel in 1st.
I think it has to do with the motor mounts. As the clutch engages in the forward drive gears the engine is "picked up" on that worn mount, and then begins to bounce back and forth until enough constant torque is applied to hold it still. As the clutch engages in the reverse gear, the engine is "pushed down" on that worn mount. Since the engine is already resting on the bottom of the mount it doesn't jump back and forth, just sits pretty.
That's my take on it. But I think the vibration is still extreme for just a mount. We'll see soon if those mounts finally show up.
