83' 300SD Shaking and clanking at pick up!

[pulix]

Hello Folks! Well, for the first time I have not a clue as to what could be causing my car to be acting as it is.....I'll explain:

Filled up the gas tank and added LUCAS Fuel Treatment (about 5 ozs. to 19 gallons of diesel)
This was on a Saturday. Car was fine until Wednesday morning, when, after riding on the interstate, started to hesitate and shudder at low speed, with lots and lots of white smoke and even black smoke when the gas pedal is pushed hard. Then I hard clanking noises and figured it must of been the additive. So I let the tank go to empty and filled up car again. At first much much better and I went as far as to add 1 bottle 12 ozs. of Redline Diesel Catalyst> (as recommended by a Mercedes tech and Diesel owner himself).
Well the car has gone back to shuddering, and shaking at low speed until it picks up to about 45-50 miles, then the shaking stops. Smoke is still present but not as much as when I first noticed the shaking.

Does this sound to be a combustion problem?
Should I have any of the engine checked out?

Please let me know your always welcome opinions...

Thank you in advance
Andrew Montoya
Orlando, Florida