after replacing the head gaskets on my 95 4rnr 3vze v6 my engine starts and idles smooth but when i give it the gas it revs up 2000 rpm and starts surging if i floor it it starts popping almost like it hitting a rev limiter? any ideas? i've double checked and its not the timing. im thinking that it might be the valve shims got mixed up when i had the heads shaved, or maybe the fuel injectors?