2005 F150 4X4 134,000 miles, I am second owner @65,000 miles. Starts/Idle and Runs Good. I just noticed after warm up/8 miles cruising at 50 to 55 mph at immediate deceleration it seems to down-shift. And when I roll/coast/stop at a red light it remains in gear but when accelerated the transmission does not hold/remain engaged unless I let up on the throttle 2 or 3 times then it accelerates/shifts fine. This condition is easily duplicated. All fluid levels are good, no leaks, no abnormal odors, and no codes when checked at auto parts store O'Rilleys. I have read some information about Slight Spark Plug Mis-Fire might cause this, which sounds strange as the engine performance is good. Any Advise is Appreciated. Thank You.

 

O'Reilly's scanners can't read Ford transmission codes. There won't be any codes if the OD OFF light isn't flashing. Spark plugs will cause a miss or shudder under light throttle application at 40-45 mph in overdrive.

 

Are you saying the transmission is slipping?

 

GLC = The OD Light is not flashing.

Roadie = From a dead stop (Red Light) yes it slips a few times.

 

What does the trans fluid level look like? Color? Smell? Feel?

 

The fluid level was high when this problem developed, but it had been high for months. To get the level down i siphoned about two quarts out with a extraction device. This did not change the condition. Fluid Color matches new/unused fluid, Smell = not burnt/matches odor from new ATF. Feel/texture same as new ATF. I spoke with a Transmission Shop today, spark plugs could cause problem on acceleration. He will diagnose tomorrow.