4.2L running like a bag of crap

I have a 4.2L with a brand new carb(nutters done) and header (feb) it has
run SWEET up until a month ago, now it's running like crap...

It's running really rich, that's the main symptom. Mileage isn't bad but
it's not as good as it was. plugs have about 10K, wires are about a year
old. it doesn't sputter or hesitate and still has great power. It seems to
run closer to normal when it's at operating temp, which makes sense.

Could this be as simple as adjusting the fuel/air mixture? Just seems weird
that "bang" it's running really rich

any help is appreciated

Jason