1999 Ford Ranger blue smoke issue

After my truck is at running temp for around 20 min and I stop at a light for a minute, or if it idles for a few miutes. When I hit the accelerator it will blow out a puff or sometimes a cloud of blueish smoke. The longer its been running the more it will puff out when I takeoff. It never smokes otherwise.

this time last year I replaced the heads and all the workings inside cause they cracked. So I know its not valves or the head gasket. I replaced the PCV valve today and it runs alot better but it still smokes when I leave a stop light/sign. Its not as bad as it was before I replaced the PCV valve tho. Im out of ideas as to whats wrong? The check engine light comes on after being on the highway for a while. My father has a code reader and he said the O2 sensor was slow to respond and its running lean. But no performance issues (yet).

its a stock 99 ford ranger xlt. V6 4.0 OHV. It dose burn a very small amount of oil between changes. About a half quart. It runs excelent besides the small smoke puffs and the check engine light.