I have a 2011 GMC Sierra 1500 V6 with 145,000 miles. For about the last 6 months or so when I start the vehicle after it's been sitting for a while, a very large plume of white smoke belches out from the tail pipe. It's a very large cloud that lingers and will float away with the wind, it doesn't dissipate quickly. Fearing a head gasket I took it to a mechanic when it stated which they advised they see the smoke but couldn't track down the source and "would hate to tear apart the engine for no reason". There's no check engine light on FY.
Fast forward to about a month a go I took it to the mechanic again for an oil change and again to check the smoke plume which I recorded and showed the mechanic. Again, he said he didn't want to tear apart the engine costing me a ton of money with no definitive reason for the smoke.
Recently a new symptom has developed, a seemingly lack of power especially when at start up when I press the gas but not so bad once it's been running. Also, my gas mile has gotten really bad. I commute a distance to work daily and have use about 1/2 tank but now seem to use almost 3/4 in the same period.
At this point since I've been to the mechanic twice I'm at a loss. Thinking about a second option at a different mechanic but thought I'd check here first.
Thanks for reading and any feedback!