My truck is hard to start in cold weather . When it dose start it won't run long

. Fully charge both batteries. Diesels require strong batteries, particularly in winter.

. Clean battery terminals and cables.

. Check all underhood and underdash fuses with a test light or multimeter.

. Check for diagnostic trouble codes.

. Check engine oil level--ensure it's filled to the top line. This affects fuel pressure.

. Check glow plugs, which are used to heat the fuel.

. Check block heater, which is used to heat the engine.

. Check fuel injectors. Take the valve cover off and look at the exhaust part of the injector when it is running. Each time the injector fires, you should see oil exhausting from it. If you see oil coming out, then the injector is good. When replacing a bad injector, take the glow plug out and crank the engine to get any oil out of the cylinder. If you don't, you could hydro-lock and bend a rod.

. Purge fuel filter or fuel separator of water. Do this at least monthly--daily, if necessary. Water can be a big problem with diesels, particularly in the winter.

. Use full-synthetic diesel heavy duty engine oil (HDEO). Installing a by-pass oil filter makes using top-quality synthetics very cost effective, when integrated with a used oil analysis (UOA) program. All engines run better on synthetics, particularly turbo diesels. Besides significantly improved engine life, turbo life, performance, and gas mileage, synthetics promote easier starting, by allowing increased cranking speed. This last factor is particularly important in cold weather. Synthetics are also easier on batteries and starter motors.

http://www.mobiloil.com/USA-English/MotorOil/Oils/Mobil_1_Turbo_Diesel_Truck_5W-40.aspx

. Check turbo--it may be coking up or turbine blades may be bent. I would only use full-synthetic diesel heavy duty engine oil with a turbo.

. Check/replace air filter. Diesels require lots of air--restricted air filters can bend turbine blades.