1990 Jaguar XJS No low end power

My 1990 jag 5.2 began to perform slugishly. I legged it home (did not overheat) Upon investigation I noticed that the hoses for the air injection ( two silicone hoses at rear of engine)were busted and blowing smoke. I replaced them along with the two rubber hoses for the manifold crossover pipe. I then started the engine and it idled better than it had in a long time. It used to idle excessively until it warmed up. Now the bad news: It took it out for a test drive and it can barely climb a hill. Once going it is okay but lacks power. I also noticed a low exhaust noise( like a small leak would sound) from the drivers side near the front of engines. Catalytic converter issue. And why suddenly after repair noted above. Need some advice / ideas.