RX8 Bogging and high AFR after 4500rpm

Hi, hopefully someone can help as I am running out of ideas. I have a 2005 rx8 231 normally aspirated, I bought the car 6 months ago and it's never run as it should. Now the prob I have is that the car runs really well and starts first time every time hot or cold but as soon as I hit about 4500rpm, the car bogs down and my afr jumps to about 19. I new the car needed work when I bought it and the plan was to fix it up and learn as I go which so far I have learnt a lot and tinkered lots (lots of cuts and scratches and swearing). since I bought it I have put new air filter, plugs and leads, coils, maf, New cat, full exhaust and new front and rear lambda sensors, New fuel pump. i have also checked the ssv which is clean and does not stick. also checked the vacuum to the ssv and it holds vacuum. I changed the ssv solenoid just to be on safe side to try to fix my issue which didn't make any difference. has anyone had a similar problem and have any ideas where I should look next? I know some might think I was mental for buying it if it needed work on it but I have done this with every car I have ever bought and have always found working on my cars to be the best way to learn about the car and I enjoy tinkering. any help would be gratefully appreciated. don't want to give in and take it to a specialist until I have no other options.