I have a 93 k1500. She's got an old tbi 350 with over 300k on it, paired to a 4l60e. I race this truck on road and off, work with it, and daily it, but keep good matinence on it. It purrs like I kitten and runs great on surface streets, then the same thing on the highway. I can get full acceleration from 70 to 90 no problem, but after 10 minutes or so you can hear a tick. Once you hear it, it doesn't get worse, but it's loud. It sounds sort of like a lifter but might just be misfire. However, once I get off the freeway, it continues until it idles for a while, or until I rev it up and hold it at about 1 or 2k rpms. (I don't have a tachometer but I know roughly where it is revving.) Then it goes away and it purrs like a kitten again. It's not valves because the first time it happened I went to adjust my valves and by the time I started adjusting the tick went away. It seems like a computer or vacuum issue because i feel it's something adjusting slowly to the change in rpms from high in 3rd to lower in 1st and 2nd. Before it would run a little rough after revving and high speeds but it's evolved into this. Other than that I have 2 slight exaust leaks which I don't think should relate unless the 02 sensor is messing things up. But I also had to replace a stud for a Rocker arm because it was pulling out of the head. It was pressfit and each time it pulled itself out a little more, it was when I was at high speeds. So in hind sight I think this problem is causing issues with my valves. All my valves are still perfect but I don't know where to start. All I know is something isn't adjusting properly, and I think its on the engine side, not tranny side. Any help is appreciated. Thanks.
