Ok, let me try to explain this. I have an '89 Formula 305/700R4. When I drive in gear there is a slight vibration in the floor board but when I go full throttle it turns into a really harsh vibration that feels like the car is bogging out. I checked the mounts, u-joints and they are good. I adjusted the trans kickdown cable and the vibration mostly went away but now the car shifts into 3rd gear before 30mph. I have some engine mods, see profile, but the trans is rock stock. ANY help with be GREATLY appreciated. Thanks

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'89 305 Formula TBI. Hedman Shortie headers, Flowmaster 80 series muffler, Jet Stage II chip, 160 thermo, Jet underdrive pulley set, Edelbrock TBI intake, 1/2" TBI spacer, Injector spacer,adjustable fuel regulator, flow matched injectors, Edelbrock TBI strut tower brace, Hotchkis panhard bar, lower control arms, subframe connectors, Bilstein shocks,MSD ignition, Edlebrock 14" open element air cleaner with K&N filter and K&N filtercharger, Auburn 3:73 Posi with Richmond gears