I just replaced my 3rd EGR valve for problems similar to yours. Like you, I had almost no power and it wouldn't build boost until I really stood on it. It did this for two days and then on the third day at idle, my temperature chime sounded, I looked down at the dash, the temperature was in the hot range and I shut it down. I let everything cool off and changed the EGR valve out (removed two screws and finessed the unit out with a couple of long handled pry bars). It had used a lot of water/coolant because the reservoir was really low, hence the temp issue and the small amounts of white smoke. New EGR valve, topped off coolant and problem solved. It had never gone out quite this way before though (always in the past it was lack of power, lots of black smoke) and at first I thought I had a head gasket problem but my pick up is fine now and isn't using any excessive water/coolant. BTW...I shopped the EGR valve around and the list is about $300, a "good" price was around $225 and the best price I found at Arrow Ford Abilene, TX was $166.
Good luck, hope you fix it for cheap!
Priscilla
180K miles now. (not me smart aleck, the pick-up)
Oh, I forgot to tell you..if your EGR valve comes out black and coked up and sooty...then you may have the problem I have had. If it comes out "wet" it's another situation entirely. If you aren't sure, show it to your diesel guy. I'm learning as I go, so I hope this helps.