Once in awhile at cruise speed 1900 rpm 57 mph or 2000 rpm 60 mph my rpm's will jump about 100 to 150 rpm. The a/c is not hooked up. My trans shop checked and the trans is not coming out of lock-up. It only does it at these specific speeds and it doesn't do it all the time. Most often on the first trip or two of the day. Also, normally on a grade of some kind. If you let off the throttle a little it will "hook-up" again and may or maynot let go again. But normally after awhile will settle down and be ok. Any ideas?? Thanks.

 

Have the fuel pressure checked.

 

Also check the brake light switch on the brake pedal. When the brakes are depressed it unlocks the tranny, and if not adjusted correct can do the same thing.

Also check the wiring leading to the transmission as it is too loose and chafes in the slipstream leading to intermittent problems and possible ECM/PCM destruction