my 87 sdl tonite going home began to lose power ,would not go above 40 ,black smoke,temp ok,oil pressure ok,eventually got down to 20 mph,had to get off of freeway,had it towed home.it has 175k,never has it overheated.too dark now to check anything.it starts and idles,but with pedal really sluggish and lots of dark smoke.im assuming filters first,but it is a 14 head-gaskeT?MAybe ip pump?any ideas where to start.ive taken alda off a year ago.

__________________
95 e320,87 sdl,79 300sd