So... I’ve asked everyone I know to ask and received different answers. Please help with my mystery problem.

my ‘06 F150 begins to stutter at 60-65mph. I’m not sure if it is a fuel to air issue or a rear diff issue or what. Here is what I have done so far: replaced throttle body, replaced cam sensors, replaced fuel filter, about to replace crank sensor (cause I don’t know what else to do), took it to the ford house who said it was my catalytic converters that were clogged. Went to a muffler shop to get them replaced, they did a back pressure test and it was 1.5 so I didn’t have them replaced. I experience no loss of acceleration power (at least no different than when I first bought the truck 3 years ago). No check engine light. One time when I had cruise set at 75 it had a cruise malfunction and threw a single misfire code. It flashed the CEL until I pressed the brake and disengaged the cruise control then it cleared up. when it’s real bad it feels like a sputter. I have 201,000 miles. Keep up with all maintenance.

Thinking about replacing ignition coils. Or checking rear diff because I don’t know what system is having the issue. Engine or drive train.

i should mention, it’s always at the same speed that I feel it and if I go 70 or above no issues. And the stutter does not reflect on the rpm’s

any ideas would be appreciated.
-Will fix it my myself.

 

spark plugs? have those ever been replaced

 

I knew I was leaving something out. Yes. This past February.

it has been idling slightly rough since I bought it but only so much so that I would notice it. That’s why I originally changed the spark plugs. Didn’t help the idle.

 

Could be an ignition coil bad

 

If it keeps stuttering you may have to take it to a garage that has a speech therapist.

 

Did you get any codes off of this thing before you started throwing parts at it?
It would also be helpful to know what engine and what trans, we are talking about here.
Given your symptoms, I would suggest to start with looking for vacuum leaks, something with emissions system (egr, phasers, failing sensor, ...)
Perhaps just take the whole inlet body off the engine and go through it. Get it out on the table. This will allow you easy access to inspect and clean the IAC valve, clean the throttle body, ensure all vacuum ports into the inlet are clean and clear, especially the PCV valve inlet, and EGR (if it has one).

Hope that helps, in some way!