Well I did the whole stroker thing! Bought a crank, rods, pistons, etc...
When I bought the crank they told me it was an LT1 crank (front neutral, rear balanced) so I assemble the whole motor and fire it up! Oh I also have converted to solid mounts (Don't even go there!!!) come to find out the crank is an internal balance crank!!! NOT AN LT1 Specific! so i had a nasty vibration at all rpm's The car was never driven. I backed the car out of the garage and pulled it right back in the motor probably had a total of 30 minutes of idle time. So I tore the whole motor down again. All new bearings! (rod and mains!) had the flywheel neutral balanced. The motor is back in the car and runs great!!... Now the problem. 2500-4500 the car feels like its going to fall apart... 4600-7000 smooth as glass and pulls like a (insert all great things thought) I know that with solid mounts its going to get a little more vibe than anything I've ever seen but Ive ridden in cars with Motor plates that are welded to the frames and they don't feel like they are going to fall apart like this does. But Keep in mind its only in that rpm Range while driving... Not in the driveway
Any Ideas or questions are welcome. I know what I think but I wanna see what other experienced builders think.

 

Did you get a bob weight and balance the RA? I didn't see that in your post. Just that you got an internally balanced crank and zero'd out your flywheel.

 

the crank was already balanced they said I did not need to have it bobbed