97 PSD with no power and rough through RPM's

[slidensidewayz]

I have a 97 PSD with some problems. When the truck is sitting still and I take the RPM's up to about 1200 it blows white smoke, stutters and coughs like a loaded up gas motor would until you get to about 2200 then it is smooth again. Out on the road you can be running about 55 and it will cut out but it doesn't stall you let off the pedal and get back in it and it is ok for a bit but it does continue to do that same thing. Recently now when it does it the check engine light comes on. When you shut it down and restart it it seems to be ok. The truck just doesnt seem to have the power that it used to. I tow a 24' enclosed trailer with a 2400# race car and probably another 2000# of equipment and it just dogs on the hills. When towing down a long run and out of the pedal when you pick it up to climb the next hill it has a long hesitation before it takes off and on one occassion it has even backfired???? The truck has 201,000 miles on it 2.5 years ago it went to Ford for similar problems and they ended up doing a fuel pump assembly. I have replaced the CPS and that was no help. Any suggestions are much appreciated.