I have a 99 Tahoe 350 at 115.xxx. It has a hard time starting but when it dose start for the day it has no problems until you let it sit overnight. I've replaced the starter, coil, timing chain, crank sensor, coil pickup sensor, fuel filter. I hook a fuel gauge up it's a 60psi with key on then drops to around 55psi while cranking. Any ideas on what it could be

 

If you have to crank it 15-20 seconds and then it starts, it sounds like a fuel pump problem. Hook up the fuel pressure gage and let it sit overnight. Sounds like pressure is leaking down.

 

The problem is it won't start or take forever to get it running. But once it starts for the day it starts and runs like a champ. And the fuel pressure is at 60 psi steady with the key on

 

The check valve in the pump assembly is bad. This lets the fuel run back into the tank when sitting. You either need a new fuel pump or install a check valve in the fuel line.

 

Well I thought that when you turned the key off the pressure would slowly leak back down.

 

That is what is happening, but its not supposed to do that. That is why it has to crank so long, it has to build enough pressure to start, and that takes a while. If you install a check valve in the fuel line, just above the rear axle, it will mostly cure the problem.

 

I put one in my 99 Silverado between the fuel filter and the gas tank. Make sure you get a check valve rated for fuel and the fuel line has to be be rated for fuel injection.