I have a 2003 Chevy Tahoe 4wheel drive it has been stalling on me I put a new alternator thinking that was the reason bcus it was already no good but the problem got worse n now it says reduced engine power n won't go faster than 30miles

. Replace the fuel filter.

. Install the same ACDelco spark plugs that originally came in the truck, if they have not been changed in 50,000 miles.

. Check for codes.