My 2003 chevrolet suburban will not accelerate past 40
throttle position sensor or throttle body is dirty or damaged.
Other causes may be fuel pressure or a plugged catalytic converter.
As Rowefast said plugged converter..... or plugged fuel filter, collapsed exhaust pipe, plugged or restricted muffler or weak fuel pump are all possible causes.
My money's on the Cat- all in!
Looking for a Used Suburban in your area?
CarGurus has 18,583 nationwide Suburban listings starting at $2,000.
Search Chevrolet Suburban Questions
Chevrolet Suburban Experts