Make sure the torque converter lockup clutch is engaging properly. By the way converters are designed, there's a 10% slippage built in that can only be eliminated by using a manual clutch that locks in at highway speed. If the transmission is not original to the truck, you're going to have to install a vacuum sensing switch and a brake on/off switch to make the TCC work correctly. When the TCC is functioning on a 700R4 it acts like a second overdrive ratio. Another trick is to install a vacuum gauge and get used to feather-footing the throttle to keep the main jets and metering rods running at the lean side of the power curve as much as possible.

BTW, there's nothing new about putting a lockup clutch in a torque converter- - - - -Studebaker did it in 1949. It was hydraulic rather than electronic, though!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!