Catylitic converter

My 98 Jimmy makes a horrid bumbeling sound when i accelerate and dies if I let of the gas with in ten minutes of starting... my mechanic said fuel injection system.. but I seriously doubt that it would have made it more than 3k miles since it started if it was the fuel injection... so, I'm left wondering if my converter is so full of crap that my engine can't breath, I mean I did drive it through a lake last fourth of july!?!? So what could it be?

It could also be the heat shield has rusted loose on the converter and ratteling.
Bob Shaw

Any check engine lights?