1997 Chevy Silverado Oil getting into radiator

About a month ago my truck started over heating and my oil pressure started to dropped. When I filled the radiator with water I noticed this thick goop coming out. I checked the oil and realized I had the "milky way" problem. This of course lead me to believe I had a blown head gasket. I purchased a new block and had it installed. About a week later I noticed my oil pressure once again was dropping and I started to over heat again. When I checked the oil level I had nothing and my radiator still had that thick goop coming out. When I consulted the tech who installed the motor he said sometimes in a new motor the oil can dissolve fast because it's working it's way threw the engine and as far as the goop in the radiator it's probably old stuff that is still trying to flush out. So I flushed my raditor out and filled my oil. Truck ran great for another week and then it started all over again. The tech said there may be a hole in the raditor tubes and this could be why the oil is getting into the raditor. So I replaced the radiator with a new one and once again throughly cleaned and flushed out everything. Again the truck ran great for about 2 weeks and now again I'm having this issue. My truck will not hold the oil. It's all being drained into my radiator which is causing my truck to over heat and my oil pressure to drop. The oil is good and clean and I do not have the milky way effect. What do I do now? Is the block I purchased bad? Is there something else I'm not seeing that is causing this issue? Please help!