all kinds of problems

i love my 95 cutlass supreme. i i just got done doing a lot of work like new head gaskets, got the heads milled, new top end gaskets, new plugs and wires, and new pcv valve. my problem is when im driving it sometimes doesnt want to take off from a dead stop. it will go but it seems like i have to floor it to get it to move. next prolbem. when i hit about 50 mph the car has a weird vibration. when i let off the gas it goes away. it seems like it would be a vacuum leak but i have checked everything. also the lifters are tapping bad. has anyone had this problem after tearing into the motor? lastly i wanted to know if the tube the goes into the air cleaner tube right before the throttle body is the mass air flow sensor. it goes from the filter tube to the back side of the motor. i recently tried to get one from a chevy dealer and about got in a fight with the guy helping me since he said there is nothing on the top of the air filter tube and that it is only on the bottom and doesnt go where i said. any help on any of these questions would be wonderful. oh yeah soemtimes it dies if i recently started it and try to throw it in reverse. ive never heard of anything like that before. thanks again

Might want to check coil packs. I have had 2 replaced (at around 120K) and your symptoms sound quite similar to the symptoms my car had initially.

how long do they usually last? i replaced all 3 within the last year. if i do need to replace them is there a way i can check each to see which one or ones it is. i dont wanna shell out the cash for all 3 if i dont need to.