Cadillac Repair: 92 Eldorado misfiring, time history, eldorado

Question
Some time back my 1992 Eldorado 4.9 was skipping so I thought I would replace the ignition wires. I did so with cheap ones and it still skipped some. So I spent the big buck on the high performance set ($120). Improved but not perfect. I replaced the cap, also with the less expensive one and that helped for a while. It started skipping again. I looked inside the cap and I could see arcing to the screws holding the coil on. So another cap...the expensive one. Replaced rotor also. I shortened the coil screws and it ran better for a while but no just right. Skipping again. Pulled the cap off and it was arcing to only one screw now. Why? Took that screw out and left it out. Not the one with the ground on it. Skipping slowly getting worse. Replaced all the plugs with platinum. No help. Checked the timing with a light and it appeared to be retarted considerably but I'm not sure if I was reading it right. Advanced the distributor and it ran worse. Knocked it back. It sounded like I could hear arcing inside the cap but see no evidence of that. It starts right up as it always has but skips over the road. Hammer the throttle and it goes but hesitates, braeks up and feels like there is a load on it. Easing ove the road you can see the rpm fluctuate slightly. I pulled the codes from info you provide on this site (thanks) and they come up as follows. The "service engine soon" has never come except when pulling codes.
No EMC codes
I039 history
I052 history
A048 history
R034 history
R061 history
EMC?
I pulled the codes twice. The first time I039 code was "I039 current" and the second time,"history".
Maybe I have to take this to cadillac but I hate to with little cash and this having 172,00 on it. But it is a good looking car with all new tires and struts. Plus I like it. Any help is appreciated.
Thanks,
Craig

Answer
Erase all the codes from the computer and drive the vehicle and see what code comes back.

Are you ABSOLUTELY POSITIVE you put all the wires on correctly and the wires inside the cap for the coil wire. Did you put the spring button and rubber "O" ring insulator under the coil ?.