My personal reaction in that situation would be to replace the truck. However, if you have the time to do the work yourself, it might be worth the effort. Consider the price you could get for it as is, the cost of a rebuilt engine and associated required parts, what your time is worth, and the cost of replacing the truck. A newer truck will probably be more reliable than yours repaired. If you don't have a lot of other diy projects, this could be a lot of fun.