worried about trans

I have a 94 k1500 burban. My trans changes from 2nd to 3rd at 3000 rpm. I was wondering if this is normal. I had the trans flushed at the dealer to be on the safeside. I just thought of another question. If you drive your truck for a long time with a cloged catalytic, what damages can occur to the engine? It happened to me. I changed it with a performance converter and of course it drives much better. Should I add add a catback exhaust system? Sorry for the long post : :biggrin: