I have a 1998 Ford F-250 with 250,000 + miles. Triton V8. It's well taken care of but lately I've noticed a sputter in the engine when driving between 45-50 mph. It not a vibration, it's the engine sputtering, I can accelerate to 52 mph or decelerate to 40 mph and it's fine.
I had the oil changed last week and also had a new fuel filter and air filter installed but that didn't help. I had a 3 part fuel injection clean done 2 months ago....so it shouldn't be the fuel injectors.
Wouldn't it sputter in all driving ranges if it was the emissions.
Any thoughts out there. It's just happens between 45-50 miles per hour. The sputter is worse if I have a load.
Thank you for any suggestions

 

You might want to try this in the appropriate year F150 forum, the '98 F250 was a "LD" - in otherwords an F150...

Could it be torque converter lockup shudder?