lack of power at highway speeds

Took a 40 mile trip yesterday down Rte 22 in PA. Its a 2 lane highway crowded constantly with trucks and under heavy construction in certain spots, with cars entering the left lane constantly. The trucks usually create a bottleneck. Needless to say, its not the fastest moving traffic. When a trucks decides to finally exit, theres a huge gap of maybe a quarter mile with the rest of traffic ahead. I try to take those opportunities to speed up and pass the right lane. It seems though that when Im going 55-65 uphill especially, the RPMs dont increase even if I push the pedal down to the floor. Im not saying that Id like the acceleration to be faster or better, there are actually points where the engine will not go any faster no matter what. The RPMS are just about 2400. What could this be? Im using Hess gas (cheapest around) and I put some fuel additive in to clean the injectors (Gumout)

The acceleration is normal from 0 or low speeds, but at highway speeds there seems to be a lack of power. On normal days I can easily get this car to 95, it flies and transmission shifts normally. Is it just the fuel or does this indicate something else?

i dont know what your problem is but i had that same problem and a couple weeks after it started i shattered a piston so if i were you i would have it checked out