94 Blazer S-10 runs rough/brakes fade/stalling

I have a 94 Blazer S-10 4dr/4x4 4.3ltr. It has 145+k miles. Recently I have had the ehaust, catalytic conv to tail pipe replaced. The old cat con. had rusted out and clogged ehaust. Next replaced alternantor. Next replaced Coil. Each one had failed in turn. Now truck runs rough even at idle. Sometimes brakes fade/fail at stop signs. sometimes stalls at stops signs with loss of power to brakes. Exhaust seems to be rich and thicker than normal. I think it might be a vacuum leak. Loping doens't change much with PCV in or out. Vacuum is prevent at pcv but it lopes also.