More Power

Hello, i have a 95 gmc with a 6.5 non turbo (yes one of the odd balls) letter "p" engine with a 5-speed. How can i get more power with out spending alot of money? i pull a 8000 pound 5th wheel with it, it does ok but when the hills come, don't get behind me. I haved the truck now for 8 years and it is been farily good to me. But with my camping habit, i need more power.