coolant loss '96 3800...0300

Before I tear off the intake...again...is there any way to know for sure that it is the culprit for my coolant loss? 18 months ago I replaced the intake due to an eroded out coolant passage. The dealer claimed that the intakes warp, but mine had eroded. I pulled the heads and a couple cylinders were full of coolant. The engine wouldn't even turn over there was so much coolant in there!
So, anyhow, I'm losing coolant big time again, but the engine starts, runs, misses...code 0300/01,02. I hope I can avoid a long, drawn out investigation...it's freezing out there!
Thanks for your input.

Pull the plugs see if there are coolant traces on the plugs, do a pressure test, all basic steps for coolant loss diagnosis.