2001 Chevy Tahoe 5.3 blowing white heavy smoke when started

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I'm running out of ideas my 2001 Chevy Tahoe 5.3 Is blowing white heavy smoke when started and bogs down when you stop at stop signs. Had block check done that came back good. Pressure 158-190 on all cylinders. Replaced valve stem seals and pcv valve. Lots of gunk under valve covers oil is clean on dip stick no white foam changed 400 miles ago. No error codes. It has used coolant but I suspect it is leaking out the front of the block near water pump. Before it was blowing white smoke when on the interstate and it was up to temp some times the oil pressure would drop to about 20ish psi and it would start making nocking sounds and would quit if you let it sit for a 10 min or so. The wired thing is the sound wouldn't go away immediately after string maybe after another minute after letting it cool down. The intake manifold gasket was replace about 1.5 years ago and so was the water pump. I think the water pump may leak off the front of the block. I'm thinking about doing a leak down test next. Any other suggestions?

I'm thinking this could be.

MAF

Catalytic Converter clogged

Rings

Computer related

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Followup after driving about 15 miles an getting it good and hot it is now burning clean. I am suspecting that getting it hot and letting it sit for a couple hours produces the issue. Could this be a fuel issue or some sensor having issues on cool down?

[gapost]

Did the gunk under the valve covers look like butterscotch pudding? If so, search for castech heads. I think 2001 is a little early for bad castech heads, but loosing coolant and gunk is a sign of a bad head. If you use the dexcool-orange coolant, you probably won't see discolored oil. But, if you have crude in the bottom of your oil pan (stick a screwdriver in the drain hole), it's probably a bad head. The low oil pressure could be a result of bad crankshaft bearings because of the coolant contamination in the oil. And others can correct me, but I don't think a bad head won't affect the compression.

[txab]

http://ww2.justanswer.com/uploads/Bluegorilla/2008-12-05_142924_Coolant_loss_5.3.pdf

 

 

http://www.agcoauto.com/content/news/p2_articleid/148

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No butterscotch the gunk was all black. It is running dexcool-orange coolant. When I had the valves out I looked for the castek logo and did not find it.