1998 Ford Expedition White Smoke

My truck (gas engine) just started running rough and white smoke started pooring out the tailpipe. The smoke has a strong smell of raw fuel unburned. When I drive the vehicle it pings and diesels and has a hard time picking up speed leaving a trail of white smoke behind. I took it to a shop and they said that I had low compression on two joining cylinders and that it needed a head gasket ($1700). I question for the time that they had it that they actually did a compression check. There is no codes, no coolant lose, no coolant or gas in the oil. No overheating. The radiator pressure checked ok. I checked fuel pressure on the rail, checked fuel injectors and harnesses with a fuel system tester. I am having a hard time accepting that it is a head gasket. Thanks for any help.