No low end power

A couple years ago,I purchased a 2001 trailblazer 250 that had recently had a new top end bored to .040. I have since installed a new 38mm(400cc) carb and a FMF fatty gold exhaust . I have also installed a EPI performance clutch kit. The trailblazer had both lower and upper power to spare for about a year. Have lots of hills that I climb, and over the last several months I have noticed a very definite decline in low end power. Barely able to make it up hills, but starts on a dime and has plenty of high end power. I checked compression;was 115 psi, after putting a little oil in, it came up to 120 psi. My service manual indicates 115 psi is spec. Again, starts on a dime, idles like a champ, just bogs somewhat on low end, just doesn't have the same take-off power, can't climb a hill for squat like it once had. Installed a new Ricks CDI box, as well as repacked and cleaned silencer,did not help. Is jetting the carb what I'm missing? I have never changed jets. Is compression too low? new rings in order? Can anyone help, I'm at a loss.