Jeep Grand Cherokee Running Rough, Starting & Power Loss Problems

Battery 3 year old but keeps draining flat whether car used or not used. Since last charging battery up from flat seat belt sign and airbag sign will not go out.

the car misses at a speed of 65-75 mph, above this speed and below the engine runs smooth. have had the injectors changed at a price , but the problem still persists. the engine is a mercades, diesel 2.7 lt. various garages have had the car...