The "shudder" you say you feel when accelerating, you "hear" any noises at the same time? The reason I ask is there really isnt anything spinning that fast yet ( driveshaft, rear end, torque convertor, trans. internals, engine) on intial acceleration.
Do you feel/hear anything when bringing up the rpm. in park/neutral? Only bring the rpm up a bit, dont rev the bags outta it when its out of gear, thats NOT a good idea for any engine.
A collapsed lifter will make the engine run like shit, like its missing at idle, it will also be a noisey tick, OR if its a roller cam and lifters, it will sound like marbles at idle, and may smooth out as the rpm comes up. What cam and lifters you running?