Rack and pinion problem?

[Yii]

I dunno where to start.... So after class one cold night i drove home. Steering felt heavy and stiff a lot more than usually. I got off the highway and discovered that when i turned the wheel it took a lot of my own strength to turn the wheel left or right equally difficult. When i gas and turn it becomes normal. I took this to the mechanic and they said it might just be the rack and pinion but they would replace the electric pump first. They did that and i've been driving it for 2 or 3 days now. Sometimes it feels normal sometimes i feel it heavy but when i park and start the car later it would change. I really dunno if its a rack and pinion problem but the mechanic said if it happens again this would be next to replace. Any input on this guys? i know its a rare problem =/