Idles perfect, but won't run over 5mph with tons of white smoke!

[powerstrokes only]

So I was at our ranch in NM this past week and my sister is having problems with her '02 7.3 dying lately. I can make it die by slamming the hood, traced the short down to some after market wiring to a torque converter lock-up kit, and a engine break, runs great otherwise. The next day she tells me she started to haul a horse out to do some work and it all of the sudden lost all power, runs rough and smokes white smoke like crazy and will only run 2-3mpg barely! She got it home, and I got in it and it started perfect, idles perfect no trace of a miss at all, try to drive and it miss's and smokes just like she said. We changed the fuel filter right away and have the same results. The funny thing is no check engine lights have come on. I have a good friend who is an ex-Ford diesel tech that we will have it towed to, but I have not been able to get a hold of him yet, so I am just curious if anybody has any ideas. I appreciate any help!

[Ozone-etr1]

i'm going with head gasket bub
no CEL because its mecanical
and not electrical yet

[nccatfan]

White smoke could also be unburned fuel. Get injectors buzz tested, and a cylinder contribution test. Look at the UVC connectors too.

[ianstew]

head gaskets on the 7.3 are pretty darn tough. i agree with ^^^^