I have a 97 with a 4.2 liter automatic 2 wheel drive. As soon as I put it in gear it begins to miss really bad and shake. It continues this down the road. It levels out a little bit at upper speeds. It levels out and runs great if you accelerate and it kicks down to passing gear. Once it shifts back up it runs rough again. Any thoughts???

 

Did you check for any codes ?

 

Check plugs? What they tell you?

Fuel, spark or compression. What is that engine missing?