How many miles on the truck? You might just need a new fuel filter. That is a really cheap thing to replace, and even if it isn't the problem, you have eliminated a possibility for cheap.

Did you replace the spark plugs as well? What kind did you use?

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1998 Mazda B2500 Extra Cab 5sp manual
(1998 Ford Ranger 2.5 liter)

Cat back with Flowmaster
Headers (no name)
K&N intake
Power Aid TB spacer
JET Performance chip
Accel coils
Bilstein Shocks
Electric Fan coming soon!