If the carb is a Holley 1bbl, then check the main jet size. Bigger isn't always better, but if it's below a 55, then it's a good bet you are lean.
What size tires are you using? Big tires can make a heavy truck into a slug. It's also possible that your trucks gearing is just not planned for what you are doing. Some more info about your trucks gearing might pinpoint the problem.
What other tune up stuff have you done? If it's missing due to plugs, wires, distributor, coil, etc. it can feel very weak.
Timing? If your timing is too far advanced, your engine will really hurt under a load (such as climbing hills). You may want to do a little reading, and I know that if you search my name, you will find several topics on it in the past few months. Important timing topics are initial timing, vacuum advance, mechanical advance, and total timing.
You may never be able to keep up to your buddy's 440 or 360, but my truck climbs hills damn good when I'm not towing a load. My special upgrades are electronic ignition, super six and free flowing exhaust. It's also a 727 automatic transmission.
I also think the yellow paint adds a couple of horsepower
