Gmc sonoma running at high rpms

[Sonomadriver]

I've had problems with it before but I've started to notice it more, that its running at too high rpm for only going 35 to 45 mph. I was going up a hill at 40 mph and it was running at about 2500 rpms. My idling rpms is about 1500. It's an automatic, and it just doesn't seems to be shifting right.. Someone please help!