Hello, I have a 2014 chevy express 3500 van with 78862 miles. It has the 6.0. If I don’t crank the van in about 10 days, I have to turn the key about 20 times to get it to crank and run. Once I do get it cranked, if I go crank it every day or two it cranks and runs fine. I have replaced the battery, starter, ignition switch and checked all fuses under the hood. I also switched relay 15 and 39 with other relays in the fuse box. I have not tried jumping the start relay because I don’t know which relay to jump, either 15 or 39 and I don’t know which two to jumper. Any help appriciated.

 

there are electrical schematics on gmupfitter.com which will probably help you.
Make sure all the positive and negative connections are clean and tight, including the ground strap on the engine.