Check engine light?

HI all I have a question to ask, I have a 99 silverado with a auto and a 5.3l 4x4 I had the check engine light come on today and I had my friend attach his scanner to it to find out the problem. well it turned out to be nothing major, But he also noticed the manifold vacuum psi was kinda high like -10" and he said that the norm was like -16". If any one knows why it is like that or what the fix is I'm sure that is causing some poor gas mileage. He was using a Snap On scanner. Also the truck hesitates badly when its cold or under the normal operating temps. thanks

You should have around 18 inchs vac at idle. Various factors can influence this such as burn't valves, worn cams, sticky egr valve, ignition timing, fuel delivery, etc, and of course a vac leak itself somewhere. Take a can of ether and lightly spray a few shots around the intake maifold to block area and where it smoothens out and increases vac reading you've found your leak if thats the case.