Car loosing power @ 60 KM speed and @ 80 KM

Hi. Grand Marquis 2004.
Problem started when one day i pressure washed the car
engine with water. After the wash the car was shaking
badly and i thought that thats sit the engine is gone. So i let
the bonet open in the sun and let it dry for a day. The car
works fine but still loosing power. I googled and many
people asked me to change the spark plug but nothing
changed than i cleaned the fuel injectors and car works fine
for a day and than the same problem. The car drives fine
but as soon as i hit 60KM guage, the car start losing power
but after pressing the gas it drives fine.

A friend of mine is pretty sure that it is because of fuel
system and i agreed because i used fuel injector cleaner
which you mix with petrol and the car starts working fine
but again just for a day or two and than back to same
problem.

I even changed the fuel filter but nothing is working. So
here is whats been done with no improvement.

- spark plug changed
- ignition coil checked
- fuel filter changed
- fuel injectors cleaned

Your kind help will be realy appriciated. Another thing i
should mention is that my car aircondition is also having
weired issue, if i kept it at low speed it automaticaly starts
running high randomly. It works fine at full speed but as
soon i turn it low it goes back to full speed and time by time
it goes down and up.