Turbo Stumble under load

I have an 05 F-350, this past weekend I was driving through the rocky Mountains and ran into what I think may be a turbo problem. I had my EGR cooler, and turbo replaced 30K ago, never had any issues in the past.

Here is what would happen:
- As I was pulling a hill My truck would "pop" a little like a gas truck that started to miss on a cylinder.
- The "popping" noise sounded like it was either coming from the waste gate, or throught the air filter.
- If I put my foot into the accelorator, making the tranny downshift, the turbo would spool up and no problem.

ANY IDEAS????