transmission troubles 05 4 cyl awd
 

I have a Tribute 2005 I AWD with 90k.
I got this situation worsen over the time: in all gears when I try to accelerate the engine will rev up and gear won't be changed until I release the gas and then it'll shift with a kick. Sometimes just a little and sometimes it feels like a gyroscope spinning in it for a second or two before the kick. And sometimes it works just fine though. I can't find the pattern still despite I've been having it for a year.
I'd appreciate any ideas on what could it be and how much will it cost for me to fix it.