between ~2000-2300 rpms the engine vibrates under load. It's pretty consistent in all gears but not so bad in 4th. It's pretty obnoxious on the highway, the car cruises pretty well at 2250 in 5th which is where it's at it's worst. Previous owner blew up the stock 305 block and replaced it with a 350 from a van, other than that, a 3" catback, and 8mm accel plug wires it's stock. Any ideas on what might be causing the shake?