I'm looking to replace my two wheel drive 1/2 ton tow rig with a four wheel F250 because I'm towing 3500 pounds. The question is, when is a 7.3 diesel done? I'm looking at two, a 1999 king cab unknown body miles but replaced 7.3 for 11k or a 2001 extended cab with 256k on the clock for 10k...