My 02 Montero XLS with 225000 miles has run like a top untill now, does not do this all the time but seems to be getting worse, sitting at idle it idles smooth, put it in drive hold the brake and starts to miss take foot off brake and take off seems to smooth out then start up a hill or get on the gas (under load) it will start cutting out like missing then it seems like it smooths out until you put it under load, I thought maybe bad gas but pretty much ruled that out but could be just cant figure how to tell if it could be bad gas or spark or ignition problem maybe, never has had new plugs wires etc..or would the cat converters cause it to miss under load? any help would be greatly appreciated..

thanks

Lee Cagle