93 F-150 oil pressure problems 302 mileage 113000

I am so lost! I am at best a shade tree wannabe. My 93 f150 has developed a sudden oil pressure problem. I recently had the timing gasket replaced and now my truck wants to die when I am not accelerating and my oil pressure is dropping. A local mechanic says the spring in or to my oil pump is weak and wants to replace the oil pump? I dont think me and my shade tree can handle this one. In an attempt to fix this I have so far, replaced plugs, plug wires, cleaned air control valve, new air filter, changed what vaccum lines I could see, kerosene motor flush, new oil pressure sensor, and I kicked the tire twice. Also when I changed the air filter there was a foamy gunk in the filter box. :Evil: The sensor seemed to work for a few minutes then the pressure slowly began to drop again. If I rev the rpms the pressure holds, if I let off it falls to zero and dies. I seem to be losing power too. All this started after the timing chain fix? This is driving me nuts. Can someone help?