just wonder'n does anyone know how long the average cat lasts? and are there any aftermarket ones out there?

 

Get some magnaflow high flow cats.

 

The two failures I've experienced were on vehicles with 150K and 250K miles, respectively. Perhaps other members will have better suggestions, but the quick-n-dirty check I use is to feel the exhaust - if there is a pulsing of the exhaust flow, probably OK. If the air flow feels continuous, like from an air hose, may want to investigate the cat or other exhaust restrictions.