Exhaust popping

[chicklin]

Well, I thought I had this thing licked but I guess not. If you've read any of these threads you'll know what I've done, but I've still got a popping noise from the exhaust.

http://67-72chevytrucks.com/vboard/s...d.php?t=370615
http://67-72chevytrucks.com/vboard/s...d.php?t=370264

The short story is just about everything has been replaced and I still have a little popping or spitting noise coming from the exhaust. It seems to only happen under acceleration, particularly under load (i.e. I can't reproduce it as easily sitting in the driveway). It also seems to get worse as it warms up.

Vacuum is 18 and steady, timing is 8 btdc, the entire ignition system has been replaced, the entire fuel/air delivery system has been replaced. The exhaust from the cat back has been replaced. The heat riser functions properly. The idle mixture was set via vacuum to 3 turns out on a newly rebuilt carb. The choke has been adjust to open fully when warm and close to about a 1/8" gap when cold. Compression is good and even all around.

It does idle a little rough. Not bad, but just a little miss every couple of revolutions. The engine supposedly has about 79k on it. It could be 179k, but I'd say that by the condition of the rest of the vehicle, 79k is not unfeasible. I don't know anything about the condition of the internals.

As far as power, it's hard to say. I've been driving an '02 Silverado for the last 5 years so I don't think I can give it a fair shake. I can run down the highway at 75 no problem and it doesn't seem to downshift much. It does feel a little sluggish accelerating, but again my frame of reference is probably off.

The only thing I haven't really checked (and what I'm leaning towards) is some kind of valve train issue. My local Chevy dealer (who I've done a lot of business with and generally trust) quoted me about $1,500 out the door for a complete top-end rebuild. Not sure if I'll get to that point, but is that a reasonable number? Short of that, what else can I check?

It's not a huge problem and I'm driving it every day on the interstate to and from work, so it's definitely getting worked, which is good. I'm just kind of anal as I know there is something wrong and that just needles at me.