I have all the related problems of a maladjusted vacuum system, which I am going to address next weekend, with the help of this forum, but I am unsure if this is also related. My transmission will not shift into high gear until I am going 65 mph, regardless of throttle position. I do not want to drive it due to the high rpm's which I'm sure diesels are against. I have to work this weekend so I will be unable to work on it this weekend, but I was just wondering what you guys think. Could it be a throttle linkage problem?