Kicks down to easy

I have a 1988 ford bronco with a 5.0L. I have a 8 inch lift with 35's.Got headers flowmasters and K@N air filer for mods.I realize it is kicking down because of mostly tires and maybe the lift. What is does is when I drive down the road in a low RpM it starts to lose speed and then when I press the pedal a little it kicks down. This is effecting my gas milege when it keeps going to different RPM's all the time. What you think can be done to stop this. :disappoin

The only real solution is to gear your truck down. The big tires effectively gear your truck higher. You will have to change the ring & pinion sets in both diffs.