GMC Repair: truck repair, intake manifold gasket, head gaskets

Question
About 8 weeks ago I had bad radiator, witch caused me to blow a freeze plug, had new plug installed, new radiator, and t-stat. Also complete oil change. Had driven truck 2001 gmc jimmy 4x4, 6 cyl. had driven truck for about 6 weeks with no problems. Then had my licence suspended for 60 days, so truck has been in driveway. First week checked levels. Oil perfect, color and amount. Coolant down 2 gallons. Added coolant, 2 days later my oil was yellow, mixed with coolant. had 3 different ideas thrown at me, intake manifold gasket, head gasket, cracked block. What do you think.

Answer
The MOST common and what I would check, would be the lower intake gaskets.
Although with the radiator failing, if vehicle ran exceptionally hot, it could be any of the items you stated. Bets advise would to have the system pressure tested and also have the block tested for exhaust in the cooling system. That would tell you if the heads/head gaskets are failed.
I hope this helps.