I have the same problem with my 01 is300 it started around 35-45k miles but I now have 70k. my miss hits around 4000 till about 5000 and it's like a wall aka rev limiter and once its past this point it good. no mil light, good milage, shifts good I'm thinking wires or coils but it could be something else I just hate to take this to a garage and get screwed when it's something I could fix if I knew what it was. Also I want to add I notice it misses worse on dry days aka like static discharge and seems better on humid days altho still misses. I thought fuel also but since it seems to pull good from 5k to 6k I can't seem to think it would be a fuel issue aka injectors or pressure.