Hyundai Forum - Hyundai Enthusiast Forums - 2000 Sonata performance problem

First, let me say that I am new to this forum and also I am new to working on Hyundai’s my 30+ experience is on air-cooled VW's so I am working my way to modern day cars.
My problem is that for some time I had a missing problem (like a dirty injector) or a plug starting to go bad. I would idle rough at stops but had plenty of power after the hesitation and sometimes a "pop" or small backfire them "ZOOM" off to the races. Then some 3 months ago I went from 4500 elevation in Nevada down to sea level in CA and it ran really poorly for a brief time. An engine light briefly came on but when I shut the engine off and jiggled some s wire and things ran fine the rest of the trip. And the light never came back on. Just the same stuff kept occurring rough idle at stops, a cough and then zoom!
Last week I was determined to force the issue sop that I could improve the problem so I ran it hard and force the engine light top come on and the scan read PO306 or misfire in cylinder 6. But when I jiggles wires and turned the engine off and then back on, the light still remained on. So, I pulled the #6 wire and held it away and I could hear the firing really good so I don't think it's a bad wire. I then pulled the plug and it was a little wide for the suggested gap so I reduced the gap to specs and replace the plug. Next, I pulled the fuel rail, removed the #6 Fuel injector. Manually cleaned it and replace the fuel rail. When I started the engine back up the light then went off and the idling was much better. But..... Now when I kick the engine into high gear by romping on the accelerator, the engine now acts as if it is chocking off and the power is reduced rather than increased. I literally need to slowly increase the speed and now the car goes upgrade only 45-50 miles per hr.
Dazed and confused any ideas or suggestions?
rhuckabay