I have a 1998 F-150 XLT 2WD with 4.6L engine with 180.000 miles on it.
And i guess I have the 4R70W

So I'm crusing on the highway and want to pass a semi or an old lady, I hit the throttle and the transmission kicks down, but will not engage the next gear at high rev. unless i step of the gas a little bit (then the turbine gives you a REAL kick)
I've heard that a "shift improver kit" such as B&M #40266 can solve my problem, but i want to know what you guys think.

 

Have you flushed out your fluid and changed the filter? You may just have some crud built up in there to where it is partially blocking a pathway for fluid to flow.