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There is no TPS setting to gain MPGs. It's either in range or not. The computer is always looking for the lowest closed throttle voltage then adjusts itself accordingly.
So you have a F250 with a 5.0L engine. Poor choice for Ford to make or anyone to purchase. Since you stated before you had a single bore throttle body I assume you swapped in an intake or complete engine from a Mustang? Regardless the TPS setting is the same.
Define "suck bad", what MPGs are you getting and under what driving conditions? Have you checked for codes. Did you retain any of the EGR or smog equipment? The more stuff you pull off then try to trick the computer the more likely you are to effectively decrease the MPGs and performance.