I too have the ES mount and all I noticed when I installed it is that I seemed to be able to "feel" more torque and the car just "felt" better. I can't explain it, but to me the car just seemed right after that....
Oh, here is a dumb question, which way does the curve in the poly material face, front or rear?

I do get a bad vibration at about 100 MPH, but I don't get to that speed often enough to worry. Besides, its probably that darn steel LT1 driveshaft. I'll replace it soon with either an aluminum or new steel shaft from a 2002.
I have since installed ES engine mounts, the car feels even better!! Still a vibration over 100......

 

A little update...

I emailed Energy Suspension a week ago when this post had just started and asked them about any recall or responses to complaints. They never bothered to write back...hmm...

 

i have to change the mount cause i hear that sound when my clutch is not ppress
should i got with ls1??
where can i get it?