If it were a clutch, wouldn't he feel a problem in all gears? He's no doubtably run the car hard in 1-3 in an attempt to figure out a problem or resolve it, wouldn't we expect an RPM blast in those gears also?
Aside from the ECM and 4/5th gear themselves, what part of the car knows what gear it's in, and could act negatively ?

 

The torque load on the clutch is highest in the higher gears, that's why a common test for early stages of clutch slippage is to get going 40 to 50 in 5th, step on the clutch, rev the engine and "drop" the clutch (or more correctly release it rapidly). It's a worst case scenario for clutch load.
Precisely why I posited spark blow out as a possible cause--there's not a whole lot of any thing different going on in the individual gears--except the the torque load on the engine (actual torque load at the flywheel, not volumetric load as calculated by the PCM).

It could be a fuel supply issue, but then as you have said he has likely been thrashing it in the lower gears, nonetheless that higher load in the upper gears will call for more fuel. A quick run with a wide band O2 system would sort that out, if not enough fuel is being delivered it would go lean when the power loss starts. Another possibility is bogging from too much fuel--again a single run with a WB O2 sensor would reveal that as well.

 

not sure what the op means by "bogs out" exactly but the fact that its more prevalent in higher gears (higher load) makes me think its ignition related. i had a weak COP that would only cause a mis if i was near WOT in 3rd or higher

 

Yeah, we probably should have pursued a better definition of "bogs out" right up front in this thread.

BTW, and for the benefit of any newcomers, what you describe is spark "blow-out"...

 

Ok basically i shift to 4th it putters into a silent idle I work the throttle nothing. And 5th I can run clean at 1900 rpm at 50mph then same problem as 4th any higher rpm.

 

Also I blew the throw out bearing on my stock clutch and replaced the clutch with a spec stage 1 a few months ago.

 

That is very odd behaviour, you need to do some data logging to see what's going on with timing and fueling--it is very difficult/impossible to diagnose things like this without someone knowledgeable being there to see, listen, and touch.

In the lower gears, if you got full WOT and accelerate, is there any drop off of power at all--right up to red line?

As the regular stuff has been put forth, you need to get it to a specialist so that the complete problem may be diagnosed...

 

It runs strong 1st-3rd till Redline no drop off.

 

You need to get it connected to a good diagnostic tool like the Ford IDS (Integrated Diagnostic System), and/or bring it to someone that has the KSAs (Knowledge. Skills, Abilities) and tools to run independent diagnostic tests and see what's up...

 

It's sitting at mustang specialties right now they said it wasn't getting enough fuel and it's running on 2 cylinders in 4th and 5th. They havnt found what's causing it yet.