05 altima losing power
 

hi all......I have an 05 altima 2.5 s, nothing fancy, 5 speed transmission, approx 105000 kms on it. the last 2 days driving, on the highway especially, i go to give it gas, and suddenly there is nothing...shift to 4th, give it gas it goes.....then nothing...same thing shift to 5th again and it goes fine for a bit....then same damn thing... it doesnt make any loud clunk or grinding noises, it almost feels like its outta gas, then when i shift gears its ok for a bit..anyone help me out with what it might be...thanks so much in advance.. Tanya