Engine burning oil

I"m having trouble with my 5.7Lr vortec engine in my 1997 gmc sierra. I can't seem to figure out what is causing it to burn up oil. I've had the engine rebuilt twice at my local garage and they've gone over everything they could think of to solve the problem, but it continues to burn oil. It will use 1 3/4 quarts to go 350 miles. They've come down to thinking that the intake manifold might not be seating down completely causing oil to be drawn into the cylinders. They are thinking of doing some machining to the manifold to get a better fit. Does anyone out there have any thoughts or suggestions to help?

Not to be a wise guy here, but they don't seem to what they are doing!! Are the plugs fouled, have they done a cylinder leak down test, if the manifold were fitted wrong the evidence would show on the intake gasket and ports.

Not to be a wise guy here, but they don't seem to what they are doing!! Are the plugs fouled, have they done a cylinder leak down test, if the manifold were fitted wrong the evidence would show on the intake gasket and ports.

Ya, all the plugs are fouling. Leak down test, not sure, I assumed they would have done that. I will have to see if they did that or have one done. Thanks for the advise.

Ya, all the plugs are fouling. Leak down test, not sure, I assumed they would have done that. I will have to see if they did that or have one done. Thanks for the advise.

I had one during that and come to find out the intake manifold was crack if it plastic that's ur problem.