Runs like a 4 cyl burns like a 8cyl

My 95 golf mk3 73k automatic 4 cyl gas its burning soo much gas and it feels like
I dont have enough power specially when im going down hill it feels
like a downshift to 1st its seems like the car automatically brakes for it self
and it dosent seem to be released until im at ground level when the check engine turns on while in the freeway going 65mph the cars runs ugly like it lacks of power and control sees rough seconds later the engine light turns off the car gains alot amount of power even feels like it has turbo in it and it uses like a gallon of water a week which is alot and its giving me 11 mpg or less