i have a 2006 lexus IS250 with a 6 speed manual tranny with about 120k on it. lately when i drive it when i go on 2nd gear i'm getting like a lag from the engine,the rpm fall down and after a second or two they go back up and it runs fine and now its doing it on 3rd and 4th and i think im starting to feel it on 5th gear also. i replaced the spark plugs and is still doing the same thing, and now it won't pull up my drive way (UP HILL) i have to start off real fast to make it up the hill please help. thanks