Lt1 vibration. Alright guys, i have an automatic 97 z28 with 108xxx miles. Since I bought it (6 months ago), it has had this vibration. It occurs at around 2k-3k rpm range in any gear including park. In drive starts at around 50 mph and gets.noticeably worse when decelerating, for example; going 70 with cruise control on then turning it off and coasting. I've ruled out rear end obviously, and transmission because i currently have it pulled but it still vibrates, so im left with the engine. The only mods that i know of to the engine are a cold air intake, edelbrock throttle body and headers, and underdrive pulley, also probably has a tune because it shifts out of first so quickly (i can put it in drive, let it idle and it will shift into second within 10-15 seconds) so what do yall guys think? Something external or internal? Thanks in.advance. -Kyle