Is your truck a 4 cylinder? If it is, it sounds like it's "jumped time"(meaning the timing is off). If you don't replace the timing belt at regular intervals (usually at 60,000 miles), the timing belt will stretch. If this happens, your timing gear can slip a tooth, throwing your timing off. Pull the timing belt cover off, rotate the engine until the number one piston is Top Dead Center (on the intake stroke) and look at the dots on your timing gears. If the dots don't line up, your timing is off. Hope this helps!