My 97 6.5 has a surging/bucking problem when going downhill only, if you are trying to maintain constant throttle position. does it either with cruise on or off. only code i get is boost sensor out of range. I have replaced vacuum lines and am considering replacing either waste gate control and /or actuator. Anyone else had this issue?

 

This is only occuring when going down hill? are you on or off the throttle? It is possible that it is a failing PMD. Do you have it relocated?

 

I have the same problem with my 97'. I got it to calm down/quit when the A/C is running. It seems to act up more when the voltmeter in the dash is sitting around 14 volts. With the A/C running the voltage drops and the engine quits bucking. I had a code once for the optic sensor and this only happened once and has not come back. I have not relocated my pmd but have been considering looking at the resistor in the harness connector.

 

Did u figure this out? I am having the same issues on a 98 I just bought.

 

No I haven't, replaced the pmd and no differnce. I notice its not as bad after it warms up a while. Almost to the point of replacing the injector pump.

 

Sounds like you guys need to replace the optical sensors or depending on year pull the optical sensors filter harness out. The symptoms you are describing are those that you encounter with the frowned upon optical bump mod. So if you haven't done that to your truck then that leaves it at either the filter harness, if you are so unlucky to have that, or the optical sensor itself.
Just my .02 here

 

what about the accelerator position sensor
im having same problem, downhill surge