so i will be as detailed as i possibly can be, feel free to ask questions and any advice will be appreciated. I have a 2006 monte carlo 3.5 non-flex fuel. The issue that i am having is that when i accelerate the car when it is under 2k rpm it seems to have very little power, it is most noticable from a stop since while its moving it will just shift down. From a stop its almost as its not reading my pedal input, no matter how much i press it it will accelerate at the same slow pace. this is only until 2k rpm, as soon as i hit 2k rpm it seems fine. this has been going on for quite a while. The car to me seems to be running lean, my fuel efficiency has shot down to about 15 and it was 23 before, my spark plugs were very dirty, so i changed them and wires and the spark plugs got dirty again. the car has no check engine light on and when you plug in the diagnostic system it doesn't find anything wrong. the transmission shifts well, the car cruises well. Ive checked the fuel pressure and it is fine. the car idles fine in park and neutral but it is rough in drive and reverse, i suspect this is just because of the spark plugs, which is caused by the unknown problem. Please i really need help as ive ran out of ideas and cant have my car running like this, any input is appreciated. Thank you

 

I have the same kind as you but I have a 3.5 with flex fuel. When i accelerate hard it sorta stays the same pace then a few seconds later it will start to accelerate hard. I dont know why though