The 3-4 upshift is a concern for most every 95-97 truck and it has to do with the torque converter clutch strategy and valving in the transmission. It unlocks just before the 3-4 upshift and relocks about a second after the shift. There are mechanical fixes for this but it is up to the hardware and software that Ford uses. The extra power brings out the condition.
The mileage increases are usually only going to be noticed while running empty as it takes a specific amount of fuel to make a specific amount of power. The extra power you thought was nice for towing is taking a little bit more fuel.
Run it for a while empty and see what the mileage does.
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Tuning, PCM flashing, and burning chips for 7.3s since 2008. Repairing all aspects of 7.3L Powerstrokes for 25 years.
Eight 7.3L PSDs in the driveway including a 1994 Crown Vic and 1973 F100/2002 F350. Looking for the next victim.
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