my son stopped by he has a 2000 cummins auto. he said it surges around 40 to 45 mph with a/c on had a new computer and a tps installed about 3000 miles ago checked all battery cables,all tight any ideas, I'm a 12 valve guy so I'm learning thanks Lee

 

Is the tach jumping up and down about 200-300 rpm?

 

Yes it is

 

The torque converter is going in and out of lockup. It is caused by electromagnetic interference produced by the alternater. If you do a search for tc going in and out of lock up you will find directions for wrapping foil on wires to shield them. It works for some but it didn't on my truck. I bought a noise isolater from bd diesel and it works.

 

Thanks getting on bd now heard something about the foil myself will give it a shot,Lee