I have this wierd vibration from the truck that I can't figure out. The truck idles smooth with no misses, however as I rev the motor from around 1500 to 2000 rpm the engine shakes bad enough to make the entire truck rattle. It revs up smooth so I don't think it is a timing problem it feels like a really bad loss of balance on something. It does it when driving/park/neutral at all temps. I have electric fans and the motor is a crate 350 with 5000 miles on it. The water pump is new, but the alternator and the power steering pump are about 2 yrs old. I also installed a new torque converter at the motor install to eliminate the stall converter from the previous build. The vibe just started one day out of the blue. I went into a hardware store and it rode fine the way there but when I started it and drove through the parking lot it began and has remained. My next test is going to be to remove the belts to eliminate the accessories and next unbolt the trans and torque converter to eliminate those. Could a vacuum leak cause this without affecting idle quality. Oh and it is TBI injected. I put 5000 miles on it and it ran awesome now this.