My F350 has this odd problem... NEED HELP!!

[CRS-62B]

Hello to all!!

First off, I love my 2004 F350 SD (6.0L Diesel, 4x4)- and many thanks to Bill for undoing the damage the stealership did when they reprogramed my FICM!!

My truck has a very odd problem: Whenever I am on the highway and I engage the crusie control the truck begins to buck and surge. I looked up the TSBs to see if there was anything that could cause these problems, and the only thing that popped up was the one that covered FICM reprogramming.
The problem remains...
I know it isn't the MAP sensor, and aside from an Edge Evo (soon to be a GRYPHON) and an after market intake I have done little to the engine. Sometimes the bucking & surging goes away, only to return a little further down the road.
Also, my MPG is lower than average (16.5 on HWY, 12-14 City Both Empty), and only seems to get better whenever the performance level on the EVO is set to Max (I had an Edge Juice with Attitude, and the MPG was better under the extreme setting).

I am at my wits end with this!! If anyone has any advice on this, or has run into something like this I would be very grateful for the help!!
Since I am getting a Gryhpon in the near future, what would ya'll rreccomend; I am looking for better MPG when loaded and empty, and a nice high power tune.

Thanks to all!!