Diesel Bombers - 6,5 td GMC sierra in France

Hi, I'm from south France, near of Nice, and I decide be a member of DieselBombers because no one, no garage can help me... Iwill resume the problem with my 6.5 td 1994 gmc 1500 sierra. My car starting well, I let engine warm before driving. When i engage gear (automatic) the car stumble/sputtering when i accelerate... like have air in diesel pressure system..with each time stumble white smoke at the exaust, impossible to drive more 20 /25 km/h , thecar make like mistfire.... 5 minutes after driving, the problem gone and the car run well.Only sometime under hard acceleration, I have like a mistfire, sometimes. About 15 minutes driving, when i use the brake pedal, or use the sterring (if i don't accelerate) my engine idle begin very low and few times after, the engine shut down/stalling.... really dangerous !! Istarted again the car, and if i don't give some accelerate, engine shut down again !!! So I unplug Ecm Coolant Temperature (near of thermosthat), and i have fast idle ( like warm_up mode), the engine stop shut down alone, and i can drive "normally". When the sensor is disconnect, sometimes i have only 3 gear, and when I have service engine soon light, I have the 4 gear. And the light, come, gone, come, gone..... I want kill this car on the road....LOL And this is EVERYDAY i have this problem, begin in september.... no garage see the problem, they don't have obd1 or anything for check... So I check if i have somme bubbles on my filter drain valve, also to the drain T. nothing. I changed lift pump (Ac delco), OPS oil pressure switch (Airtex), vacuum pump 1 year ago, fuel shut off solenoid 2 years ago, glow plug 6 month ago, PMD 2 years ago with a resistor number 9, with a cooler plate locate to my front bumber for cooling. Also my car have 280000 km. I bought 4 years ago. From canada. I don't know what i can do , or buy for repair. And I have to use my car everyday...:argh: Thanks to people can take a little time for helping me. thanks again §:tu: