Pebo

Hello all, brand new Mercedes w208 clk 320 owner, and oh boy has it been a project. Been checking boxes and fixing it up. One problem i cannot figure out is my high long term fuel trim of 15%-20% both banks. At first i thought it was a vacuum leak(still could be), made a make shift smoke machine, didnt find anything. I read here that if you raise the rpms the fuel trim should level out to 0. Mine does not. Stays constantly high at all rpms and cruising. However if I floor it, it will dip down for a second and imediatly raise back to high. I cleared out the pcv channels, replaced those hoses, cleaned the egr, replaced every vacuum line i can find, new fuel filter, cleaned MAF sensor and throttle body. Did a fuel pressure test, a solid 56 psi. Had a p0300 code at one point at high RPM, have not been able to recreate. Running out of ideas.Any help would be greatly appreciated