astro van error code: P0420,P0101

Sir.
I have a 2000 chevy astro van, cargo, 4.3 ld engine. has rough running after start up, and engine service soon light stays on. presently the engine has 156000, miles on it. browered an service code reader to read error codes, code is P0420,P0101. lets back up and review history of this astro van, bought it used was fleet van. had two years notice problems with transmission, got that repaired, then last winter engine was shutting down, found shorted out coil, replaced, coil and solid-state power drive module with coil, porblem showed up during pa winter.
at presently have bad fuel milage and sulgish on cold start-up's, fouling spark plugs going jet black, changed o/2 sensor under drivers side, no change. here's a clue, after starting up pulling out sometimes the astro van will not go up to speed as i press the aceration pedeal. clue two as i pull out astro van speeds up then jerks forward then back like some ran into the back of the astro van.
please advise
astronightmare

you'll get more responses in the correct forum! Does the 02 switch, is the fuel pressure correct? is it bleeding off?