92 Chevy G20 4.3l 6cyl. Won't start. :-(

[thuffner3]

Hello all,
I'll try this again. I have 92 Chevy van G20. Last week while on a trip from Cincinnati, to Louisville. She started to hesitate at medium power at 65 mph. When I say this, Medium is between no acceleration and full on the throttle. Well we make it there and she blowing black carbon like no tommorrow. This clears up after a short time. I make it back under poor running conditions. I replace the cap and rotor, plugs and wires. She somewhat better but not great. I take her to my local Mech, he tells me that I had two cracked plugs. Fixed this but was informed that my baby should have an engine flush. I didn't have this done. The van ran great for almost a week, then on a return trip to Louisville the problem returned. I came back to Cincy. Performed a compession test to find out that the cylinders were reading extremely high. 210 psi plus.
So I took the heads off. Everything was caked with carbon. Cleaned everything up. Replaced the valve seals. seated the valves. Put everything back together. Now she won't start.
She has tried to start. I've gotten a couple of backfires. She did run extremely rough for about 20 secs.

I cleaned up the old plugs(only 150 miles) and used those. Could it be fouling?
Perhaps a semi clogged Catalytic converter?

Help

TIA

Neil

[thuffner3]

Got her running, partly fouled plugs. and a bad MAP sensor.