Well it looks like I'll be heading back to the dealer once again. After going the first time for lit service engine and wrench lights,I was told there was nothing wrong. They said they would wait for the update codes from ford. Well the truck seems to be driving funny lately. While doing around 70mph on a slight incline on the highway the truck will 'lag' about 300 rpm then jump back up then lag etc..All this while maintaining constant foot pressure on the gas. When I let up on the gas it will drop 3-400 rpm instantly with a thump. And also the cruise control stopped working. What the @#@*? 2500 miles. Anyone have any thoughts about this?

 

It might just be a vacuum hose. The old cruise controls worked off of vacuum.

 

You stated that the service engine light came on.
When this happens the computer goes into a fail safe mode to try to protect the powertrain.also all safety related items go into failsafe mode.Cruse control is safety related so it is disabled until the repair is made.The cruse control will work again when the problem is repaired.

Mike

 

Thanks for the info. Can driving while in fail-safe harm the truck?

 

The Ford engineer that my sercice dept. talked to said you won't hurt your truck driving it in failsafe mode. Eventhough it rides like *****.

 

your description of the problem sounds like a torque converter lockup clutch issue.