1994 GMC Suburban 1994 Suburban Engine check light, cuts of

Hello
I bought a Suburban 1994 diesel. Few things don't work.
1. Overdrive doesn't work.
2. When speed is 65 miles/hour comes check engine light on the dashboard but car drives without any problem. After restart check engine light disappears.
3. When engine is cold starts normally but later cuts off fuel. And I have wait about an hour to start it again.
Thanks for response because I live in London UK and is great problem to repair car like this.