Blown head gasket?

So yesterday I went to get some lunch and notice what appeared to be a puff of white smoke from the tailpipes. At the end of the day on the trip home the engine seemed jumpy ,low coolant & service engine lights on. Poured nearly a full bottle of coolant which didn't fill the Rad. Started up & SEL flashed for a few miles. Temperature got extremely hot.
There is gunk on the radiator cap. About 2 years ago I replaced the UIM, LIM, thermostat, hoses & rad. I bought a used Plenum & am sure the "stove pipe" is leaking.
Does this sound like a head gasket issue? It's a 98 GP GT, NA. Thanks!

Does this sound like a head gasket issue? It's a 98 GP GT, NA. Thanks!
It sounds like a good theory. You just need to prove it. I would get the coolant system filled completely up again and find out where it goes. It could be that it is being blown out the overflow tank. If it is, blown head gasket. You can also make sure it's full and remove your radiator cap and start it. See if bubbles come out. If there are some coming out, blown head gasket. Another trick is to have it sealed up and start it and see if the coolant system pressurizes immediately. This also would pint to a head gasket.

I agree with RKVONS on this.....don't just assume it's a head gasket.....it's very rare for these engines to develop head gasket problems.....

You have gunk on your rad cap, because you were low on coolant and when air and Dexcool mix, that gunk is the end result.....

You need to refill the system and burp it.....best way to do that is with one of those Lisle funnels.....

http://static.summitracing.com/global/images/prod/mediumlarge/lil-24680_ml.jpg

You fill the funnel just to the bottom......start car......fluid will drop.....fill just to the bottom of the funnel......as car warms up, that level will start to rise....do not worry......it will rise a couple of inches.......then when the thermostat opens, the level will drop quickly.....now add coolant(50/50 mix) until once again there is coolant at bottom of funnel....when coolant starts to rise in the funnel, then remove funnel and install radiator cap......make sure there is coolant in the reservoir at least to the cold line......

Now look for EXTERNAL LEAKS......especially at the radiator, the water pump, the rad and heater core hoses, and the heater core.....

Why in the world would you replace the lower intake gaskets, and then install a used upper plenum? That used plenum could be leaking......

Wow! I didn't realize it's been a month since I posted this. My apologies for taking so long to reply. I've had a lot come up in a short period of time.

Thanks for the tips. And to answer TechII's question about the plenum, it was a matter of cost at the time. It was in far better shape then the part it replaced. I figured I'd get 2 years out of it and now here I am.

Of course the UIM was leaking, the LIM gasket was leaking at the corners and possibly along the top edges where the LIM gasket meets the cylinder heads, and the rear valve cover gasket was also leaking.

With all of this I decided to go all the way and replace the head gaskets too thinking it would be pretty straight forward. Yeah right. I'm not loving the 3800 II or GM much right now (I'll rant about that another time). I'm finally at the point of pulling the heads and now have a new question.

Should I have coolant in the 4 head bolt holes along the outer edge of the head? This the bolt hole on the far drivers side, front head:
http://i43.photobucket.com/albums/e357/williebling/My%20cars/DSC07709_zps54bed3c6.jpg

Coolant poured out when I removed the bolts. If it's normal, how much coolant should I expect when I pull the head? If it's not normal could it be the sign of a cracked head?

I didn't want to experiment with it and have to clean up puddles of coolant at this time night. Thanks again