Why would pistons still be knocking

If oil and oil filter were just replaced? Now it stalls at all stops and turns. This year started off with my truck needing to have the engine timing belt changed and the timing for it set due to the fact that I just replaced the water pump. Took it in for the timing to be fixed.

After getting the pickup back, it seemed rather slow on the take off. I thought that may be a result of having the timing fixed. The a few months later steam would rise out from under the hood. My thought was the water needed to be changed out. Found a loose hose in the overflow tank caked with a sludge of oil inside and out.

Cleaned the overflow tank out, eventually replaced the radiator due to pin size holes that developed around the neck near the cap, and put on new hoses. Steam still rose from the engine when I would get home at nights in 100+ weather.

So yesterday, after two oil changes this year, my engine starts knocking as if it is low on oil. So I did what any normal guy would do - add more oil. On my way home it progressively became louder.

Checked the water. It was a tad low. Oil level was more than fine. This morning I changed the oil for the third time this year and flushed the water out for new water and antifreeze. Went off to work and nearly every stop and turn, the engine would stall.

At this point, all I can think of it the oil pump and filter, but I have no idea where they are located on this beast of a truck, nor how to replace them once I do find them.

Does anyone know if I am diagnosing this correctly, and if so where are these parts and how do I replace them? - 1989 Toyota Extended Cab Pickup 4x4, 3.0 engine, 6 cylinder w/AC