I have 2004 chevy silverado that runs good until it gets to about 45 to 50 mph then it acts like it wants to stall out

any codes? need to scan first

You mean take it to dealership? Was hoping to avoid that exspense

Not to the dealership, most shops can scan your vehicle, Auto Zone will do it for free

Thank you

Normally has a rough shift going up hills or around 45-50 mph. When we first drive it for about 20 minutes it does great. Could it possibly be plugs and plug wire? Or a vacuum leak?

With plugs or wires no working correctly you will have a misfire, blinking check engine light and probably several malfunction codes,like i said you need to retrieve the codes first to really start diagnostics, also if the fuel pump is old or the vehicle was not used for long time the problem could be Fuel Pump, you really need to test your fuel pressure after 20 min. if the fuel pressure is low or border line, truck will run rough and will not have power.