Rough Idle

My truck was running fine, then it lugged a few times then did not lug. Eventually it did not quit lugging. The idle was bad but in reverse or drive it was worse. It shook the truck. As far as acceleration I would compare it to when a vehicle runs hot and goes into limp mode. It does however have enough power to get on up and get to speed. At driving speeds it is fine. I took it to the shop, they replaced plugs and wires and said I have a cylinder that is out. I got it back and decided to drive it rather than putting a new motor in it. I was driving and a puff of smoke came out (blueish if I had to say). Then the truck ran fine, no issues, the engine light stopped flashing and actually went off. It ran great for about a day, Then it went back to its old ways. I had to juice it the next day and once again a puff of smoke and it was fine. As for now if it is running bad I stomp on it and smoke and great again.

The mechanic also said my compression was like 25 psi. I am hoping for the best but prepared for the worst.

Thanks