Engine lose power and rpm uphill

Hi Guys ! really hope I can find some salvation here (stuck in a town in Chile without much of honest mechanics or ones that now now to deal with my car, thanks a lot ahead for your reply !!

I am stuck with a new issue on my 1997 1.4l Opel Astra station.
The car has 190K (kilometers)

Issue Description:

- The engine will lose power and the rev's will drop down on steep inclines what will resolute shifting down gears
- If I reach an incline (but not an extreme one) with a good momentum the rev's will not drop and the engine will handle it good and even manage to speed up the hill
- If I reach a sharp incline the rev's and power will drop, it can drop from 80km/h to 30-40km/h
*Pushing the gas paddle all way down will result shaking, engine stutter and rev's and speed still drops down

- Starting an incline without a good momentum/from zero will result a very low speed and and huge effort out of the engine
*usually in steep inclines I will have to shift between 1st and 2nd gear (mainly 1st)
*even if the revs are high on 2nd gear, shifting up to 3rd will result a rev's and power loss and shifting back down

-Cruising/accelerating at flat surface will not result any problems unless I try to push to gas paddle all way down - that can make few small jumping feeling and engine stutter like I mentioned before

Other related information:
- Issue started appearing after the last work by the last mechanic (compression issue on the 4th piston) fuel filter have been changed as well
- yesterday I brought the car to another mechanic that denied compression issue, also the engine didn't had problem while we disconnected each Cylinder separately
- Exhaust has some exploding sounds on idle and it sucks air once in few seconds (did the $ bill test) (burned/loose exhaust valves can cause this ??)
- Catalytic have been replaced
- Check engine is not on

Last mechanic suggested it is slipping clutch but it's not sound 100% to me since the issue is not noticeable when there is not high load on the engine and the revs go Down and not up while the car loses force

What is your guess? what should I check first ?

If you want to test the clutch go out on a straight stretch of road and short shift every gear. Get into 5th (or 4th or whatever your top gear is) at a low speed and smash the throttle. If the revs go up, but the speed doesn't then your clutch is slipping.

Your car doesn't lose power when going uphill. For a set rev range in a set gear your car has the same amount of power on the flat as it does going uphill.

This is the problem, because going uphill you have an increased effect of gravity acting on the mass of your vehicle i.e gravity is trying to pull your vehicle downhill as you progress up the hill.

This is a net increase in the forces working against your car and your car's engine. If you're approaching a hill that you know that your car struggles on then you probably need to drop a gear and increase the rev range that you're using as you proceed up the hill.

You probably already noticed that your vehicle gained power as you go down hill and you possibly need little or no throttle at all. This is because gravity is now pulling the mass of your vehicle downhill, a net decrease in the forces working against your car.

As a general rule of thumb which ever gear you need to use to comfortably get up a hill, is the same gear that you should be using to comfortably and safely get down a hill.