Mustang Running Issues Part 2

Has a 1990 GT Engine(All Stock) From the day I put the engine in the car, it has ran like this and shakes violently.Worst at 1000rpms. Won't rev past 4000rpms. When you let off the gas(feels like an earthquake. I've replaced upper and lower intake gaskets, checked vacuum leaks, Good Fuel Pressure(37psi when engine is running, 41.5 when pump runs and engine not running), New wires, plugs, Swapped out distributors(didn't help at all), Timing is accurately set 10btdc, firing order is correct, cam timing is accurate. All 8cyls have good compression, all injectors pulse/spray, all 8 spark plugs fire. My next step is replace motor mounts. The viberation can be felt all through th car, all 4 wheels, anywhere on the car. I've also swapped out TPS, Air bypass Valve, EGR Valve and no improvement. MAF sensor is good and clean. I have no check engine light on when the engine is running. If anybody can give me a diagnosis that would be great. Thanks.