Bought a 99 XLT, Flex fuel 3.0, 92K miles. Pings at 2800-3200 rpm under light to medium load. Not throwing any codes. Also have a short "flair out" like it's flattening out about 3800-4000 rpm under a heavy load, lasts about 2 seconds, then picks up again. I have replaced the DPFE, the EGR...