Options for a truck rookie

[PJsthnam]

To start, my traveling brick is suckin' the gas right out of my wallet. It'a a DD (I need a truck for work) so she may have to go. I don't have the kind of cash to put in a newer motor, or rebuild with better internals, or trans swap, or gear vendor, etc. What I might be able to do soon is buy another cheap truck then sell the 72 to try and recoup the money. I want a full size truck (I'm 6'1) and american made. I really don't want to new of a truck. The 72 has a 350 w/ 400 tranny (3/4 ton). I know the newer (80's or 90's) trucks can get better milage, but I was wondering what kind of milage a 50's or 60's truck with a straight 6 six and manual (would prefer auto) tranny would get. Any input would be greatly appreciated. Good or bad. Thanx in advance.