u/AceTennis10

Hey everyone, looking for help diagnosing an issue with my 2000 Ford F-250 Super Duty 7.3 Powerstroke.

Truck info:

•	2000 F-250 7.3 diesel

•	\~290,000 miles

•	Automatic transmission (4R100)

•	Has an aftermarket “turbo dial” / tuner in the cab (not sure of brand)

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Main issue:

•	Truck will not go much over \~68 mph

•	When trying to accelerate past that, RPM suddenly jumps from \~2000 to \~3000

•	Feels like it hits a wall and won’t accelerate further

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Behavior details:

•	RPM jump happens suddenly under throttle

•	If I let off the gas, RPM drops back down normally

•	No check engine light

•	No flashing OD light

•	Happens consistently under load

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Tests I’ve done:

Test A (steady acceleration):

•	From 55 → 65 mph

•	RPM went from \~2000 → \~3000

•	Once speed stabilized, RPM dropped back to \~2000

Test B (light throttle test at ~60 mph):

•	Let off gas → RPM dropped quickly

•	Got back on throttle → RPM jumped to \~2000

•	Then after a few seconds dropped and stabilized around \~1500

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Other observations:

•	I can clearly hear/feel the engine working harder when accelerating

•	Sounds like normal turbo/diesel noise, but noticeable when the RPM flare happens

•	Truck otherwise drives fine at lower speeds

•	Temp gauge currently not working

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Suspicions:

From what I understand, it seems like:

•	Torque Converter Clutch (TCC) is locking/unlocking

•	Possibly slipping under load

•	Could be:

•	Failing torque converter

•	TCC solenoid

•	Or something related to the aftermarket tuner

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Questions:

1.	Does this sound more like a worn torque converter or a TCC solenoid issue?

2.	Could the tuner/dial be causing weird shift or lockup behavior?

3.	Is the \~68 mph limit possibly a governor/tune issue?

4.	What would you check next before replacing parts?

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Next steps I’m considering:

•	Setting tuner to lowest/stock setting

•	Possibly removing tuner completely and retesting

•	Transmission fluid/filter service

•	Solenoid replacement vs full torque converter

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Any help or experience with this would be appreciated. Trying to avoid throwing parts at it blindly.