i'm justwonderin how well the1999 5.3 engines hold up with high mileage. do the have problems when the reachhigher miles (125,000) or are they still strong and last long if well taken care of

 

They last a lot longer then that with proper maintenance as will most all modern automotive power-plants.

I routinely see fleet vehicles with this engine go over 300,000 miles still running well and not consuming oil.