1999 gmc 1 ton
I have a 1999 gmc 1 ton dually. It's 2 wheel drive. All of the sudden on a road trip the trans started to slip. Now it will go about 50 miles on a cold start then start slipping. I have changed the filter and fluid and it still only goes about 50 miles then starts up again. I can only go about 55 once it starts acting up. Please advise. It is a automatic trans.