1997 Ford Explorer • 158,000 miles

My 1997 ford explorer 4.0 5r55e automatic tranny 4wd has a shifting problem no codes no blinking o/d light. The truck drives perfect when I first start it especially in the morning it last about 15 mins. When warmed up and at a stop I hit the gas pedal and the truck seems sluggish and revs higher then normal and sometimes wont shift to the next gear unless I let off the gas pedal then shifts fine after that, until I have to make another stop. I feel like its not downshifting to first when I stop but when I manually shift it to 1st gear then to drive it seems fine. Also when driving along at steady speeds 35 or 40 mph it keeps shifting gears up and down? Once in awhile it does downshift and drives smooth while warm. All other gears work fine just 'drive' when its warmed up I got it check at a local transmission shop and the guy thinks its a speed sensor I think its the valve body or solenoids I would like another opinion.
September 6, 2013.

I would test the vacuum going to the shift modulator on the left side of the trans. If its good replace the modulator.

Sep 6, 2013.
Thank you for your reply, i'll get that looked at!

Sep 6, 2013.