I just got done measuring the compression in each cylinder. All cylinders were between 120 and 135 except the number 5 cylinder, which was at 70. So what the heck do I do now (BTW this is my daily driver)? I am guessing that the problem with compression can come from a bad seal between the piston ring and the cylinder, or a bad seal at the valves. Since all of the other cylinders are good, do I just live with it? Is it worth pursuing any further? Anybody have any suggestions? Background as to why I was checking in the first place: The guy I bought my truck from owned it for about a month or two, but the guy befroe him has owned the truck since '73. The guy I bought the truck from said that the motor had been rebuilt by the guy he bought it from (the long time owner), but he didn't really have an idea of how many miles ago. Being that the truck has about 220,000 miles on it, the rebuild could have 25,000 miles on it or 125,000 miles on it. Before I started making any changes to the motor, I wanted to have an idea of what I was working with. Eventually, the goal is at least 300hp and 400ft/lbs--fun but still reasonable for DD reliability. I am debating whether I should be saving up to get an entirely rebuilt motor, or if it would be appropriate to build this one as I getmoney for parrts (intake and carb, then heads, then cam, etc.). Thanks for your help.