Vibration in engine, and lack of full power

This 97 Z71 K1500 standard cab short bed step side with a factory steel cowl induction hood is a fine example in emerald green metallic. It was a truck that my son bought. After he ran it dry of oil, it became mine to settle his bill. The motor was to far gone to rebuild so I decided to buy a new GM Performance 350 CID L31-R 9.5:1. While I was at it I added a set of BBK shorty headers and a 1"throtle body spacer. While apart gasket matched exhaust ports and smoothed them out for better flow. Installed a new clutch and pressure plate. The 1st time I went to start it  stopped cranking. After all the checks you would normally make, battery, starter,   ect. I decided to pull the spark plugs and found that # 5 cylinder was full of gas. Drained the oil/gas, and squirted oil into #5. Pulled the top of the intake off laid rags in around the fuel injector and powered it up. The fuel regulator was leaking and the fuel ran down #5 runner. Replaced the regulator and put it back together again. It started but was not running right. Took the upper plenum off again. This time I laid out the fuel injector on a towel hook up the electrics and with a remote start button, cycled the engine and checked each injector. Some did not have a good spray so I replaced the whole injector set. The truck ran better. But soon started to get different trouble codes. When the o2 sensors showed up I installed 4 new Bosch wide band O2 sensors. Several other engine sensors where replaced. It ran okay but never the way it should. There was always a slite vibration and a sense that the engine was choking. after three years of use 11000 miles started to get misfire codes and the truck was running rough. This prompted me to do and ignition upgrade. Summit racing billet distributor, new high voltage coil, 8mm wires , and new crank sensor. I already had Bosch double platinum plugs, and they all checked okay. In came the whole Cam/Crank relearn thing. After straitening out the timing I took the truck to Chevy to see if they could reflash the computer. While there the tech thought the cat might be blocked. So I put on a new stainless steel replacement Magnaflow set of catalytic converters, and while I was at it I added a Magnaflow stainless steel cat back exhaust. Still have the underlying vibration, and the problem is different. At 1500-2100 is a miss or stumble. I believe that the truck is running rich. if you accelerate to 2500-3000 rpm it runs a little better but the vibration is still there. The 1st question is this In the later Firebird's and Camaro's you had to buy a flywheel-clutch-pressure plate set that was balanced together, was it the same for the trucks? Has anyone made any of these upgrades had smooth operation issues. Compression is between 175 and 185 psi per cylinder. Because # 8 was the lowest at 175. I pulled the heads to check. there seemed to be a heavy build up of carbon for only having 11000 miles. after replacing the head gaskets, and seals. made another compression test and that cylinder was still reading 175. I did replace the plugs with AC Delco, but it made no difference.