Hi All, I have a 99 F150 XLT 4.6. 122,000 miles

I am wondering what Tranny is behind my engine:

I am having a slight problem when accellerating on the highway, the truck seems to "slip gears" nothing too harsh, it seems to operate fine off the highway.

I had the tranny serviced when I bought the truck last year.
(fluid change and inspection)

I got everything I need to tune it up (plugs, wires, fuel filter, pcv)

Just wanted to run it by eveyone to make sure I am headed in the right direction.

TIA

 

It is a 4r70w transmission.
Alan