Hello all, maybe someone can steer me in the right direction...

i bought this this rig (from a national rental company) a couple days ago and had a 200 miles drive back home. I jump in and start making my drive and about 10 miles into my journey the truck starts bucking on acceleration , as if it’s starving for fuel, could not get over 50 mph. I take it back to the selling company’s yard and they ordered a fuel filter. Their guy did the change out with me watching. The old filter did mot seem bad as he used the fuel in it to fill the new filter, but it’s is hard to tell sometimes. He also took off the little pre filter and it looked a bit dirty and he cleaned it out, it looked to be a serviceable, small inline filter.
I take off again and it runs great...for about an hour then it starts acting up again, same problem. By being extremely light on the throttle and going maxim 50 MPH (35 going up hill) I finally make it home 6 hours later.
My question, I suspect it has a bunch if trash in the fuel tank or maybe a bad injector pump ? I am going to drain the tank today and look at the fuel real close and look in the tank. If the fuel is OK would a bad pump cause this problem you think? or?

thank you for any input or suggestions !
rob