I don't know much about the mustang you have. I think you should keep it though if you can afford the insurance, gas, etc. As for a Ford F250, if you need a truck just for working with buy an old one. I owned three Ford F250's - '77(caught fire-totalled), '78(wrecked), and a '79(sold to get a 4X4 in Alaska), loved them all. I also bought them all used.
Basically the Fords were great for what I needed them for and I never paid over $2,000 for each one. The older trucks are WAY easier to work on and cheaper with insurance. They were for the most part TOO big though. The 400ci would drink gas in a hurry. If you like to play games, go ahead and join the "Chevy vs Dodge vs Ford vs GMC" debate. I've seen good and bad trucks come out of each of those factories. I currently own a '92 Dodge Dakota (my first Dodge was a '77), and it has over 100,000 miles both highway and offroad, and it's been a GREAT truck!
WSmac