Surge at highway speed

[healyvct]

Thanks for helping me out first off. I tried to find the problems I am having and cant quite find anything like what I am experiencing. I have 7.3 2000 Excursion that is surging at highway speed. Runs fine until around 65MPH. Then it surges and sputters. Runs fine on the streets. I have edge programmer. I turned it back to stock and still have problem. I also have watched my oil temp and when I get up to the highway speed it starts going crazy. Also when the surging starts. It read 40 degress then 180 degrees. It flashes all over. I just changed my oil after this started. No help.

Thanks for your help,