1998 Ford Ranger engine cuts out

About 6 months ago my mechanic rebuilt the top end of my ranger. It seemed to run fine at first with the exception that when I would start it up in the morning I got what seemed to be a large amount of moisture coming out the exhaust. Now it seems like there is some blue smoke mixed in there also, when it does this. But the main problem is that my truck cuts out. It will go days without cutting out and then it will start cutting out and maybe cutout 2-3 times on my way home which is about ten miles. It seems more likely to happen when I"m going uphill. I've taken it to my mechanic when it has been cutting out and then it won't cut out and he says that he can't fix it until its actually cutting out while he has it. I took it to another mechanic who fixed some things and didn't cut out for a couple of days but continues to do so. I wouldn't be too concerned other than it's almost winter and I don't know how the slick roads will handle the cutting out. I've tuned it up with new spark plugs, rotor, cables.