Won't start when cold, hard and sluggish when warm

got a GMC Sierra 2500HD diesel. Truck will not start when cold. After checking batteries, and fuel pump. Still wouldn't start. Sprayed ether and started right up. Ran it for a bit shut it off and ran it again. Did this a total of 15 times. On 16 was very sluggish starting up. After I shut it off would not start. Hooked up my scanner and it threw a U1000 code. Am thinking it's something to do with the FICM. Any suggestions
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