losing power

Hello everybody, I started noticing a loss of power when i accelerate, I was going about 80mph in 5th gear and tried to pass another car, when I hit the gas I noticed a very significant loss of power, after a few seconds I get the power back. If I downshift into 4th gear It accelerates fine, I...

When I first start the car, its good and gets going fine. I drive it for about a minute, whether it's cold or warm already, and then it starts shuddering and jerking and losing power, like it's going to stall. If I gas it, it hesitates and eventually pulls itself out of it. It does this for...