1996 discovery 58,000 miles, battery went dead, wasnt old anyway maybe 2 years, so through town at 35 to 45 miles a hour it stays charged but at 65 mph for about 2 hr on the road the battery dies car runs terrible i have to pull over put it in park till it charges back up , i just replaced the battery and altinator, and cleaned all terminals ,and it still does it, i can run all week at 35 mph no problems but when i get on the highway...problems...whats going on?? a relay???
thanks for your help..

 

Have you done a alternator/battery load test, if not go get it done at one of your local auto parts stores, most of them don't charge.

 

i had the belt changed a month ago it seems to be on right, its a good year gatorback is this the problem???could it be slipping