I have a 98 4x4 and just yesterday it started acting up while out getting dinner and threw the codes listed in the title... i proceed to drive it home slowly with it idling real rough, sluggish take off and running smoother at a mid rpm and the sel light comes on at 25mph and starts to flash @ 40mph. i changed the plugs and wires with ac delco wires and autolite platinum plugs, the previous tune up was done less than a year ago which included a new ac delco cap, bug, wires and autolite plugs. after the new wires and plugs still have the same issue as before with no change so if anyone has ideas please lend me a helping though

 

still sounds like a cap and rotor botton to me. the 4.3 are bad for that. I had to replace the one in my s10 in less than 25,000 niles. I would remove yours and look at the contacts. But i would not drive it if your check engine light is flashing. you could do some real bad damage to the cat. converter.