Need some technical advice please guys

[Not ready yet]

Decided to pay a visit to theNorth Yorkshire Moors today, all was well until I had a sudden drop of power going uphill and engine sounded like shite and refused to do more than 2.5k revs, being AA recovery member I continued to our destination in Bedale and parked up oil was ok, but nearing minimum.
The only thing different I had done was to treat it to some Shell V power fuel, other than normal supermarket fuel, but saying that I had travelled 100 miles before the problem started.
Limped back to Wetherby services, topped up oil (10/40 semi), and set off back home.
Serious loss of power on the uphill stretches, but kept at 50mph on the straight but still restricted to 2.5k rpm.
100 miles later, heard a small click and the car shot as normal and has been right since.
Did have an aftermarket CAT fitted last month, the old one had broken up. Just wondering if any pieces had blown into the back box causing this problem or sensors not fitted correctly.
It is a 1997 1.9 version.

Thanks

Terry

[BladeRunner919]

I think you need to get the codes read in INPA or similar, otherwise you'll just be working with a lot of guesses. Have a look at the sticky thread for forum members with diagnostics and you may have someone nearby.

[Mugs]

my cat broke up a few weeks ago and i had exactly the same thing. it wouldn't go above 30mph at one point. i took the cat off and found pieces blocking the pipe. new cat and 2nd hand rear silencer fitted and all is well again.
i suggest you you take off the exhaust and give it a good blow out with an air line.