If your vehicle is showing vehicle struggles to reach or maintain highway speeds, here are the most likely causes and the parts you'll need to fix each one.
At highway speeds, the engine requires maximum fuel flow. A clogged fuel filter or a failing fuel pump will starve the engine of fuel under high demand, preventing the vehicle from accelerating further.
A melted or clogged catalytic converter acts like a potato in the tailpipe. The engine can expel exhaust gases fine at low speeds, but at highway speeds, the backpressure chokes the engine, causing a severe loss of power.
The MAF sensor measures incoming air to calculate fuel delivery. If dirty (often caused by over-oiling aftermarket reusable air filters), it underestimates airflow at high speeds, causing a lean mixture and power loss.
Worn spark plugs or weak ignition coils might perform adequately at low speeds but fail to produce a strong enough spark under the high cylinder pressures and demands of highway acceleration.
If the engine revs up but the vehicle speed does not increase, the transmission is slipping. This is often due to degraded fluid, a clogged filter, or worn internal clutches failing to hold highway gears.
On turbocharged engines, a loose hose clamp or cracked charge pipe lets pressurized air escape before reaching the engine. This causes a massive loss of power at higher speeds and is a frequent error after recent engine work.