1997 Chevy Truck Hard starting

Code 1870 is transmission slipping so have a trans guy look at that. He could tell you better. If you check your fuel pressure that may be your problem. Your truck may be one that had the harness problem to the fuel pump. If it was it should have had the correct harness added and it would change the connection on the fuel pump as well as adding about a foot of new harness being spliced in. After your turck sits for 8-10 hours check your little valve on the fuel line on the intake. It will look like a tire valve. If there is pressure it should shoot up if you try to bleed it. If it doesn't it may be the fuel pressure regulator as well so it would be better to have a pro check this out.