Thank you for the prompt replies.

The computer issue is something I suspected as being a problem but I was not sure if the air was injected in Open Loop (before normal temp is reached) or closed loop (after normal temp is reached) mode.

Since my truck has the rail injection for the head it appears I maybe causing more problems than I solve in I disable the air pump system.

Oh well, have any of you been successful in finding the cause of the bucking between 40-50 mph? I have looked through the forum and the possiblities are endless. Some have added a restrictor plate to richen the mix, but why is the mix lean? I suspect a vaccum leak somewhere or maybe a weak spark?

Any help would be greatly appriciated....this is a very difficult problem to track down.