Escort clx gas problems and hissing from the exhaust

Hello together, have the following problem I’m just normal as usual with the car on the highway with an average of 160 driving at once I notice a strong power drop and a hissing from the exhaust or from the region where the exhaust is located. If I don’t give a gas the engine is quite normal. Faster like 130 I can’t drive now let alone uphill I have to switch down to the 3 gear so I can get up to some extent. I have to say the car doesn’t belong to me but to my girlfriend and I don’t have any idea of cars either. Maybe someone has an idea what it might be? Ps: Guilty people that there are so few punctual characters in here and that the gramatics is so bad but had to write it with an iPhone because I don’t have a pc here. Greeting Dennis