I have a 91 pickup with the V6 and 4wd. I live in Boise with pretty mild winters.
All winter long with temps below 35 the truck had blown HG symptoms (Losing coolant, white smoke out tail pipe) so i parked it and and bought a little focus to drive through winter. About 2 weeks ago i went and fired it up. No white smoke drove it to the grocery store it was surging and shaking while driving at low rpms. So i looked under the hood and saw the spark plug wires were from 1991. I decided to give her a tune up. Put some NGK V power plugs and cheapo duralast wires in there. Viola fixed the shakes. Plugs looked alright besides all being around .080 gap from wear and tear. One had part of the insulator blown off. After driving it about 30 miles all the coolant is still there. Wondering if anyone else had a similar issue

 

Also the plugs from cylinders 5 & 6 had what looked like oil on the wire side of the insulator. I did change the oil it was dark dark brown and had a little amount of white goo on the oil cap.

 

Glad you got the rough idle/low rpm sorted out!

The old issue does sound like a failed HG to me, maybe after sitting for a while the gasket "reset"? If so I would imagine you will start to see the " disappearing coolant" issue again soon... Keep an eye on your oil for coolant, and keep an eye on your coolant for oil and hopefully everything just fixed itself :p

 

I also used a block tester and results came back negative. Bluest fluid ever. Anyone want to buy a truck?