I do have full exhaust. 3 inch flowmasters exit out the rear. Buddy is having similar issues. Really the only common thing between engines are the stealth heads. I did notice that on those heads where the push rods go thru them there is just a hole for the pushrod they are not"open" like a cast iron head. Dont know that that makes any difference just an observation. Im going to change the oil noting the amount and do the leak down test. I did pull the breather and pcv valve they are extremely close to the baffle in the valve cover about 1/8 inch