Motors and gas mileage

["Ralph Perez" <camrjp@domain.elided>]

I would appreciate the comments of anyone who has experience with the
following:

1.  gas mileage and performance of the IH 345 compared to the 304.
2.  gas mileage and performance of a IH 392 with the 345 heads.
3.  gas mileage and performance of the stock 392.

I need a combination that can handle a combined gross load (trailer wgt plus
contents of truck) of at least 6,000# decently with 4.09 gears and 32" BFGs.
Transmission is the T-19 with D-300 Xfer.

I know this group is not a bashful one.  Fire away and thanks.

Ralph