paulcal24

hey everyone, i am a new owner if a 2001 camaro z28 som it has slp dual duals, ory, lpp longtube headers and a 4l60e with a b&m tranny cooler and yank 4000 stall,......ok now ive had it for 3 weeks and now all of a sudden when i am in drive it shifts through the gears perfect when i am in 3rd gear it is fine until i slightly let off the gas and cruise it feels like an additional shift or lockup,,not sure? and the rpms drop almost like going into overdrive at like 30 35 mph and i hear a loud vibrating noise and i have to like give it half throttle just to get it to shift out of 3rd gear and if i let off the gas completly it feels like the car pushes back and forth like it is shifting up and down until i come to a stop and then go..it goes through the gears perfectly until like i mentioned above...any ideas what it could be? i am seriously worried please help thank you!