2005 Dodge Caravan No codes and poor engine performance

Ok here is the issue. My van is getting very poor gas mileage. It is around 12-11 mpg. When I accelerate the engine start out just it is only when I get to 4000 rpm in 1st. That the engine starts pinging as if it has hit the revlimiter and backing down and will not shift into first and it does this in every gear. I did have a code for the egr valve which I replaced. It did take me several months to replace due to monitary issues. I also performed a tune up and gapped the plugs at about.053. At 1 point I got an engine light for engine misfire with no specific cylinder. Now the engine runs great at idle and starts great even at very low temps. It seems as if the timing does not want to adjust at higher rpms. PLease Help my wife is getting on my case that I can't get the car fixed. I am a mechanic. I work on diesel truck so you can get technical with me and I will understand. Thanks