I have a 99 Tahoe 350 at 115.***. 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 then slowly drops to 0 over time. Any ideas on what it could be