transmission shift solenoid?

Hi,

A friend told me i need a sensor for my transmission but i forgot what it's called (shift solenoid? ) Symptoms are, as it is going up a steep hill it's seeking 3 rd gear from overdrive. Halfway up it finally connects. All other times it runs great. Any ideas?
Thanks

That may not be an issue, it could downshift to 3rd on a steep hill as commanded by the pcm, based on tps, maf, speed sensor and map inputs, I would check this out further.

Oops sorry, forgot mention it bucks 3 or 4 times before it drops into 3rd gear.

it would be the 4-3 downshift solenoid. "the part you are trying to think of" but like maxwedge says that is not to say that is your fix.
Many things are looked at when the car downshifts, even a rpm change of 300-400 will diss engage overdrive so it seems to be electrical to me.
You have any Dtc set?