1995 Other Toyota Models Lubrication System

2.7 liter 4 cylinder Tacoma. I just finished replacing a warped head due to overheating. It runs great except the oil light on the dash comes on "randomly". I say randomly because I have yet to determine a pattern. It has plenty of oil. I changed the oil and filter after repalcing the head and determining that the engine was running properly. When the light came on the first time I drove it after installing the new head, I shut it down and after checking the oil level and visually inspecting the engine, I started it back up and no light. It came on a few miles down the road and same story. A few more miles and I stopped at a parts store and added some detergent additive for the oil thinking some debris or varnish needed to be broken up. When the light came on I could also hear the head/valves chattering. After adding the detergent it seemed fine back home (20 or so miles) until I got off the interstate and it came on again. Same story, shut it down and checked everyting and when I started it it was fine. Went to town and got some engine gunk-out product which you add and run the engine for 5 minutes and then immediately change the oil and filter. Seemed fine initially. This time I raced the engine a bit and the light came on very shortly after. This time I shut it down and started it while still coasting and no light. Let it sit overnight. Drive 120+ miles today on interstate, taking it easy on cruise control. No light and all sounds good until I let off the gas approaching a light and the light comes on. Again, while coasting at 30 mph I shut it off and start it immediately and no light. It flickered once more when I let it idle at the mail box but when I merged onto the road it was fine. I keep thinking there must be some debris clogging and causing drop it oil pressure. I don't have an actual pressure gauge so I can't reference the gauge when the light is on but I can sure hear the head when its on. The owner's and reference manual are no help. What's the answer?